Corvetteforum: Q-Jet Problems and Tips

lars
Senior=20 Member

2588 posts [100%]
Lafayette=20 Colorado

Q-Jet = Problems and=20 Tips

6:04=20 PM 11/11/2002

Over the years, I've rebuilt and = tested several=20 hundred Q-Jets; I've done over 140 just in the last = year.=20 Doing this, I've seen a lot of problems, issues, and = plain=20 weird things on these carbs, so I thought I'd share a = sampling=20 of the things I've found wrong with these carbs with = all of=20 you. As you rebuild your own carb, some of these = issues might=20 be things for you to watch for.

As always, if any of you have trouble with your = Q-Jets, or=20 if you need any assistance, feel free to drop me a = note....

So here we go.... Q-Jet Problems I have seen (and = that I=20 can remember right now...):

Missing Fuel=20 Filter
Results in: Lack of a fuel filter will allow = dirt=20 and debris to get into the carb. This often unseats = the=20 needle, resulting in severe carb flooding. I have also = seen=20 this cause severe sediment build-up in the float bowl, = with=20 eventual plugging of metering orifices, resulting in = poor idle=20 and other performance problems such as jammed power=20 piston.
Comments: A lot of Q-Jets have had their = filters=20 removed. People seem to think that the little filter = in the=20 carb must be very restrictive to fuel flow, so they = toss it=20 and install an in-line filter. Eventually, somebody = removes=20 the in-line filter, but never puts the in-carb filter = back in.=20 The in-carb filter is actually very good, and does not = produce=20 a flow restriction.

Missing Fuel Filter Spring
Results in: A missing = filter=20 spring will allow dirt to completely bypass the = filter.=20 results in same problems as a missing fuel=20 filter.
Comments: These springs are commonly lost = during=20 filter changes. Many people don=92t see a purpose in = the spring,=20 so they leave them out. I=92ve also heard people say = that the=20 spring makes the filter =93block off=94 fuel flow, so = they remove=20 it. The spring is essential for proper filter = operation.

Stripped Fuel Inlet Threads
Results in: = Inability to=20 tighten the inlet fitting with resulting fuel = dripping/leaking=20 onto the intake manifold.
Comments: Very common on = the=20 pre-=9275 carbs with the smaller diameter inlet = fittings. I=92ve=20 seen people try to epoxy the fittings in place. This = never=20 works. There are also over-sized self-tapping fittings = available that can solve the problem temporarily, but = these=20 fittings will also strip out. There are O-Ring type = adapters=20 that can be used to seal up the inlet system, but = these=20 fittings do not allow use of the in-carb fuel filter. = The only=20 way to properly repair this problem is to have the = inlet=20 machined and tapped for a HeliCoil thread insert.

Damaged or Broken Fuel Inlet Fitting
Results in: = Fuel=20 leaking at carb inlet. Fitting cannot be tightened = enough to=20 stop leakage.
Comments: It is actually possible for = the big=20 1=94 Hex fitting at the carb inlet to break = internally. The=20 cone-shaped inner seal surface breaks loose from the = wall of=20 the fitting, making the fitting appear to be a 2-piece = assembly. It is also common for the cone-shaped inner = seaing=20 surface to be gouged, scratched, or damaged, making it = impossible for the flared tube end to seal against it. = Replace=20 this fitting if there is any damage.

Missing Inlet Fitting Seal
Results in: Fuel = leaking at=20 carb inlet. Fitting cannot be tightened enough to stop = leakage.
Comments: The early Q-Jets use a black,=20 rubber-coated metal seal ring up against the hex nut = part of=20 the big inlet fitting as a fitting seal. Later Q-Jets = use a=20 white plastic seal ring at the end of the fitting = threads as a=20 fitting seal. These seals =96 not the fitting threads = =96 seal the=20 fitting. There is no point in using Teflon Pipe Tape = on the=20 threads to seal the fitting if these seals are = missing.

Stripped Inlet Seat Threads
Results in: A = loose/stripped=20 seat in the float bowl will allow fuel to leak by the=20 needle/seat assembly. Mild to severe flooding can = result. Poor=20 idle. Poor hot-start.
Comments: Degradation and = stripping=20 of the seat threads is common in the older Q-Jets =96 = especially=20 the ones that have been commercially rebuilt and = sandblasted.=20 I often see carbs with the seat epoxied into the = stripped out=20 float bowl. Epoxy will not hold the seat in the bowl = for very=20 long. The problem can only be fixed by machining and = tapping=20 the seat inlet threads for a HeliCoil insert.

Damaged/Leaking Needle/Seat
Results in: Mild to = severe=20 flooding and rich-running conditions. Poor idle. Idle = mixture=20 screws will be non-responsive. Hard to = hot-start.
Comments:=20 It doesn=92t take much to cause enough damage to a = needle/seat=20 assembly to make it leak: A piece of debris passing = through or=20 damaged caused during a previous rebuild process can = easily=20 make the assembly leak. Replace the assembly anytime = the carb=20 exhibits flooding or fuel control problems.

Needle Retaining Clip Incorrectly Installed to = Float=20 Arm
Results in: Flooding, poor idle, poor = hot-start, fuel=20 puddling in bottom of intake after = shut-down.
Comments:=20 This is one of the most common assembly problems I see = on=20 Q-Jets. GM actually issued a Service Bulletin on this = subject=20 back in the late =9160s because GM technicians were = doing the=20 same mistake. There is a small retaining wire on the = needle.=20 The float arm has two holes in it where the needle = interfaces.=20 People think the retainer goes through the float arm = holes.=20 Fact is, the retainer slips over the rear edge of the = float=20 arm, and must not be installed through the holes. = Installing=20 the retainer through the float arm holes results in = the needle=20 and/or float jamming.

Float Level Too Low
Results in: Hesitations, = sluggish=20 performance, poor idle mixture screw response, surging = at=20 cruise, =93flat=94 feeling going to wide open=20 throttle.
Comments: Different year Q-Jets have = different=20 float level requirements. The early carbs all have a = factory=20 spec of =BC=94. The late carbs have much lower specs = at about=20 .420=94. Setting up an early carb to the late spec is = a common=20 mistake, and will cause performance problems. = Personally, I=20 prefer setting up the early carbs to a float level of = .275=94 to=20 .375=94. I run the late model carbs at .400=94 - = .410=94.

Float Level Too High
Results in: Flooding, fuel = coming=20 out of accelerator pump shaft hole, leaking air horn = gasket,=20 fuel discharging out main discharge nozzles at idle, = fuel=20 dribbling down venturi after engine shut-down, poor = hot-start,=20 hesitations off idle, poor fuel economy.
Comments: = See=20 comments above for Float Level Too Low. Often, late = model=20 carbs are set up to early model specs. This results in = poor=20 performance on the post-=9275 carbs.

Incorrect Float Installed
Results in: Flooding, = fuel=20 coming out of accelerator pump shaft hole, leaking air = horn=20 gasket, fuel discharging out main discharge nozzles at = idle,=20 fuel dribbling down venturi after engine shut-down, = poor=20 hot-start, hesitations off idle, poor fuel=20 economy.
Comments: Over the years, several = different floats=20 were used on the Q-Jets. These floats had different = geometry=20 with differing float arm lengths and different float = lengths.=20 Some floats can be interchanged, but this will result = in=20 binding, sticking and improper needle control. I also = see a=20 lot of aftermarket brass floats used in Q-Jets. The = original=20 carbs came from the factory with NitroFill floats. = Brass=20 floats do not behave the same. Be sure to install a = correct=20 NitroFill float when you work on these carbs. Echlin = makes an=20 exact reproduction and correct replacement float.

Fuel-Logged Float
Results in: Flooding, fuel = coming out=20 of accelerator pump shaft hole, leaking air horn = gasket, fuel=20 discharging out main discharge nozzles at idle, fuel = dribbling=20 down venturi after engine shut-down, poor hot-start,=20 hesitations off idle, poor fuel economy.
Comments: = Older=20 NitroFill floats can actually become fuel soaked and = start to=20 float lower than intended. This has the same effect as = raising=20 the float level. Replace the float any time you = rebuild the=20 carb.

Float Binding Against Power Piston Tower
Results = in:=20 Flooding, fuel coming out of accelerator pump shaft = hole,=20 leaking air horn gasket, fuel discharging out main = discharge=20 nozzles at idle, fuel dribbling down venturi after = engine=20 shut-down, poor hot-start, hesitations off idle, poor = fuel=20 economy.
Comments: During rebuilding, it is easy to = bump=20 and bend the arms on the float. If the arms are = squeezed=20 together, the float arms can rub against the power = piston=20 tower, and this will restrict float movement. In = severe=20 conditions, it will prevent the needle from ever = seating,=20 resulting in severe flooding. It is also possible to = bend the=20 float arms such that the float itself rubs against the = walls=20 of the float bowl. This causes the same problem.

Incorrect Main Jets
Results in: Hesitations, = sags, poor=20 performance, ineffective idle mixture screws, poor = idle,=20 surging, poor mileage, poor vacuum, sooting out the = tailpipes,=20 poor starting characteristics, stumbles, poor WOT=20 power.
Comments: =93Creatively jetted=94 Q-Jets are = more the=20 norm than the exception. Be sure you know the stock = and=20 correct jetting configuration for your carb before you = ever=20 begin chasing problems. Always start with the correct = stock=20 jetting setup before you start tuning, and keep = changes=20 conservative: The boys and girls who designed these = things in=20 Detroit put a lot of work into the jetting = configuration on=20 these carbs, and they actually knew what they were = doing=85

Incorrect Primary Metering Rods
Results in: Poor = idle,=20 rich idle, ineffective idle mixture screws, surging at = cruise,=20 poor mileage, poor cold-running characteristics, = hesitations=20 off idle and/or at cruise, poor manifold vacuum with = resultant=20 ancillary problems.
Comments: See comments for main = jetting=20 above.

Incorrect Secondary Metering Rods
Results in: = Poor WOT=20 performance, sags or flat spots going into the = secondary side,=20 car =93falling on its face=94 somewhere in the = secondary range,=20 smoke at WOT.
Comments: Since the secondary rods = are so=20 easy to change, they are frequently used as the = =93primary=20 tuning tool=94 on a Q-Jet. This results in some pretty = strange=20 rods being installed. Make sure you know which rods = are stock=20 for your application, and make changes in small = increments=20 from there.

Incorrect Power Piston Spring
Results in: Poor = idle,=20 rich idle, ineffective idle mixture screws, = hesitations and=20 stumbles.
Comments: At some time, there must have = been a=20 popular article published that told people to cut = their power=20 piston springs to hop up their Q-Jet: I see more cut = springs=20 that you can imagine. A cut, or soft, spring will keep = the=20 power piston seated in the full lean position during=20 part-throttle power, resulting in a sag and poor = throttle=20 =93feel=94 during part-throttle acceleration. In = contrast, if a=20 stiff spring has been installed, the piston will never = seat,=20 and the carb will be running in a full-rich condition = even at=20 idle. This causes incredible tuning problems for idle = and=20 off-idle performance, and the idle mixture screws will = have=20 little effect. New power piston springs are available = in packs=20 of 10. If you suspect the spring to be non-original, = stick in=20 a new one to eliminate this as a problem.

Jammed Power Piston
Results in: Poor idle, rich = idle,=20 ineffective idle mixture screws, hesitations and=20 stumbles.
Comments: The power piston can be jammed = in=20 either the full lean or full rich position, producing = the same=20 symptoms as an incorrect spring. You can test the = power piston=20 with the engine =93off=94 by inserting a thin, long = screwdriver=20 down the bowl vent in the air horn. You should be able = to=20 depress the power piston and feel it pop back up. A = jammed=20 piston is usually caused by dirt entering the bowl, = but can=20 also be caused by carbon sooting up through the intake = manifold from bad valves or valve timing problems.

Bent Primary Metering Rod Hanger Arms
Results = in:=20 Flooding, poor idle, hesitations, poor throttle = response, poor=20 fuel economy, ineffective idle mixture screws, sooting = out the=20 tailpipe, plug fouling.
Comments: If the primary = metering=20 rods were not engaged properly into the main jets = before the=20 air horn was installed to the fuel bowl, the rods will = bend=20 and this will also bend the piston hanger arms. If the = arms=20 are not bent back to their correct and original = position, the=20 primary metering rods will be pulled up out of the = jets into=20 the full-rich position, if they engage in the jets at = all.

Bent Primary Metering Rods
Results in: Flooding, = poor=20 idle, hesitations, poor throttle response, poor fuel = economy,=20 ineffective idle mixture screws, sooting out the = tailpipe,=20 plug fouling.
Comments: If the primary metering = rods were=20 not engaged properly into the main jets before the air = horn=20 was installed to the fuel bowl, the rods will bend and = fail to=20 engage into the main jets. This causes a severe rich=20 condition.

Cut Power Piston Lower Stop Pin
Results in: = Hesitations,=20 stumbles, poor idle, surging at cruise, ineffective = idle=20 mixture screws, hot running.
Comments: Many (not = all)=20 Q-Jets have a lower stop pin in the power piston. This = pin=20 rests against a cam in the throttle plate, and = determines the=20 lowest (leanest) position for the power piston. = Cutting this=20 pin results in the primary metering rods seating too = deeply=20 into the main jets, severely restricting fuel flow. = Again,=20 there must have been an article published at some time = telling=20 people to do this=85

Incorrectly Set Power Piston Stop Height
Results = in:=20 Poor idle, rich idle, ineffective idle mixture screws, = hesitations and stumbles.
Comments: Post-=9275 = Q-Jets have an=20 adjustable power piston stop that determines the = lowest=20 (leanest) position of the piston. Raising or lowering = this=20 stop outside its limits will adversely affect all = performance=20 parameters of the power enrichment curcuit.

Incorrectly Adjusted Secondary Rod Hanger = Height
Results=20 in: Lean secondary performance, flat spot going into = the=20 secondaries, poor WOT power.
Comments: It is common = for the=20 secondary rod hanger to not pull the rods up out of = the=20 metering holes adequately. This produces a lean = condition with=20 associated poor power. The distance from the top of = the choke=20 rear airhorn wall to the center of the rod holes with = the=20 secondary airvalve in the wide open position should be = 41/64=94.

Incorrectly Adjusted Secondary Airvalve
Results = in: Car=20 falls on its face when the gas pedal is pushed to the = floor,=20 sag going into the secondaries, flat spot going into = the=20 secondaries, jerk or delay going into the=20 secondaries.
Comments: Very common problem. The = secondary=20 airvalve is adjusted using the slotted head screw at = the=20 secondary airvalve lever, and this is released using = the allen=20 head screw up underneath the airhorn. Spring windup = should be=20 =BD to =BE turn.

Jammed secondary airvalve
Results in: Poor WOT = power and=20 performance, car falls on its face going into the = secondaries,=20 flooding going into the secondaries.
Comments: It = is a=20 common problem on the Q-Jet for the two back screws in = the=20 airhorn to have been tightened so much that the = airhorn is=20 distorted in this area. This distortion will jam the = secondary=20 airvalves, preventing them from opening. When the = secondary=20 throttle plates are mechanically opened (pushing the = gas pedal=20 to WOT) and the airvalve is jammed closed, manifold = vacuum=20 will suck fuel right out of the secondary discharge = nozzles=20 with no airflow going through the secondary side. To = fix this,=20 the carb must be removed, and the displaced metal must = be=20 filed away. Often, the secondary airvalve plates must = be=20 loosened and re-aligned to assure a bind-free = operation.

Incorrect, Missing or Damaged Secondary Airvalve=20 Rod
Results in: Car falls on its face when the gas = pedal is=20 pushed to the floor, sag going into the secondaries, = flat spot=20 going into the secondaries, jerk or delay going into = the=20 secondaries, flooding during cold-start, erratic fast=20 idle.
Comments: The secondary airvalve rod is one = of the=20 most misunderstood parts on a Q-Jet carb. Owners see = that the=20 rod is holding the secondary airvalve closed when the = engine=20 is running, so the rod is either removed or bent. The = next guy=20 who builds the carb installs an incorrect rod, which = really=20 screws up the secondary airvalve operation. On early = Q-Jets,=20 this rod also operates the choke vacuum break system, = so=20 removal or bending of the rod prevents the choke from = cracking=20 open during cold-start. This causes flooding and rich = running=20 in cold weather operations.

Cracked or Warped Air Horn
Results in: Fuel = leaking=20 around air horn gasket, poor idle, ineffective idle = mixture=20 screws, erratic idle, fuel discharging out main = discharge=20 nozzles at idle, hesitations & stumbles, poor = throttle=20 response.
Comments: Very common on older Q-Jets: = The two=20 forward carb hold-down bolts have been tightened so = tight that=20 the entire top of the carb is warped or cracked. Once = this=20 happens, the airhorn no longer seals properly to the = float=20 bowl of the carb. This causes leaks in the idle = transfer fuel=20 circuit between the airhorn and the bowl, effectively=20 eliminating the entire idle circuit in the carb. It = also=20 causes the gasket to be ineffective in sealing the = rest of the=20 airhorn to the bowl, resulting in fuel leakage around = the top=20 of the carb. No fix for this =96 buy a new carb.

Wrong Air Horn Gasket
Results in: Poor idle, = ineffective=20 idle mixture screws, erratic idle, fuel discharging = out main=20 discharge nozzles at idle, hesitations & stumbles, = poor=20 throttle response.
Comments: Use of the incorrect = airhorn=20 gasket can result in blockage of idle bleed air = passage and=20 blockage of idle fuel passages between the float bowl = and the=20 airhorn. There are several styles of airhorn gaskets, = and many=20 of them look very similar. It=92s a good idea to lay = the airhorn=20 gasket you=92re going to use onto the float bowl and = visually=20 verify that all the holes line up.

Plugged accelerator pump transfer holes in air=20 horn
Results in: Off-idle stumble or hesitation, = hard=20 cold-start.
Comments: There is a tiny transfer hole = that=20 runs horizontally in the air horn, just inside of the = actual=20 accelerator pump discharge orifice. It is common for = this to=20 be plugged with some type of debris, especially in = carbs that=20 have been sitting around for a while. If this passage = is=20 plugged, there will not be any accelerator pump shot.

Jammed accelerator pump check ball
Results in: = Off-idle=20 stumble or hesitation, hard cold-start.
Comments: = This is a=20 common problem in carbs that have been allowed to = =93dry out=94=20 for a while. Sediment in the bottom of the fuel bowl = will lock=20 up the check ball as if it were set in concrete. This = will=20 prevent any accelerator pump discharge.

Accelerator Pump Rod Installed in Wrong Hole in = Pump=20 Arm
Results in: Off-idle stumble or=20 hesitation.
Comments: There are two holes in the=20 accelerator pump lever arm for the lever arm rod to = engage=20 into: Inner and Outer. The outer hole produces a = leaner pump=20 shot, and can cause a lean stumble on engines = requiring a=20 robust pump shot. Corvettes and performance cars = always used=20 the rich, inner pump arm hole.

Jammed accelerator pump
Results in: Off-idle = stumble or=20 hesitation, hard cold-start.
Comments: This is = becoming a=20 common problem. The alcohol additives in modern fuels = are not=20 compatible with the materials used in many accelerator = pumps=20 (even some of the pumps in brand new carb kits). This = causes=20 the pump plungers to swell up and to seize in the pump = bore.=20 The spring on the pump shaft still allows the shaft to = move up=20 and down, making it look as if the pump is = functioning. But=20 the pump itself can be seized up solid in the bore = with the=20 shaft working just fine. To fix this, you must install = a pump=20 that is specifically compatible with alcohol.

Worn accelerator pump
Results in: Off-idle = stumble or=20 hesitation, hard cold-start.
Comments: Common on = older=20 carbs and on carbs that have been allowed to dry out = (vehicles=20 stored without being started through the entire winter = season). The rubber plunger material will dry out and = shrivel=20 up, making the accelerator pump completely = ineffective. The=20 pump must be replaced.

Missing idle bleed restrictors
Results in: Poor = idle,=20 ineffective idle mixture screws, off-idle hesitations, = very=20 high idle required to keep engine from dying when = placed in=20 =93drive,=94 fuel discharging out main discharge = nozzles at=20 idle.
Comments: Different Q-Jets have different = idle bleed=20 calibrations. Part of this calibration is the = installation of=20 some brass restrictor orifices in the venturi = area/booster=20 ring area. Many commercial rebuilders will actually = remove the=20 orifices during rebuild, causing too much air to be = pulled=20 into the idle fuel circuit. The engine will then only = idle if=20 the idle speed is run up into the transition & = cruise=20 metering circuit. This is a difficult problem to = diagnose and=20 correct, since some Q-Jets did not use the = restrictors, and=20 replacement restrictors are not serviced separately.

Emulsion tubes fallen out of air horn and laying in = float=20 bowl
Results in: Poor idle, hesitations, odd &=20 inefficient performance.
Comments: It is very = common on=20 older and high-mileage Q-Jets for the air horn = emulsion tubes=20 to fall out and end up in the bottom of the float = bowl. These=20 tubes assist in the emulsifying of the fuel mixture, = and will=20 cause a notable decrease in carb performance when they = fall=20 out. The can be re-installed into the air horn and = tapped into=20 their fully-seated position with a small plastic = mallet.

Plugged idle air bleed transfer holes in float=20 bowl
Results in: Poor idle, idle mixture screws=20 ineffective, fuel discharging out main discharge = nozzles at=20 idle, erratic idle, high idle required to keep engine = running=20 (engine dies when idle speed is = decreased).
Comments: The=20 Q-Jet has supplementary idle air bleed holes in the = throttle=20 plate just below the primary butterfly plates. These = bleed=20 holes assure that the engine is allowed to pull enough = air at=20 idle to keep it running, while keeping the throttle = plates=20 closed far enough to keep fuel discharging through the = idle=20 metering circuit. The bleed holes act like the = =93drilling holes=20 in the butterflies=94 trick that so many people = advocate. The=20 air for these holes is transferred from the venturi = area of=20 the carb through two small holes in the outer plenums = of the=20 float bowl. For some reason, it is very common for = commercial=20 carb builders to plug these transfer holes with = aluminum plugs=20 or rivets. This dramatically changes the idle = characteristics=20 of the carb, and frequently destroys the entire idle = and=20 cruise mixture control. If you see these plugs = installed,=20 drill them out and set up your carb the way it should = be.

Leaking well plugs
Results in: Hard starting = after the=20 car has been sitting for a day or two. Flooding and = black=20 smoke when hot-starting.
Comments: This is a = grossly=20 over-rated problem. It is not by far as common as some = articles and publications would have you believe. The = Q-Jet=20 uses soft metal plugs to seal off the production drill = passages in the bottom of the float bowl. The passages = are=20 drilled and plugged under the main metering jets and = under the=20 secondary metering orifices, usually referred to as = the=20 primary and secondary well plugs. The primary well = plugs are=20 visible from the bottom of a fully assembled carb. The = secondary well plugs are only visible and accessible = once the=20 throttle plate is removed from the float bowl. If = these plugs=20 leak, the float bowl will run empty after sitting = overnight,=20 and all the fuel will end up inside the intake = manifold. You=20 can test for this condition by simply removing the = carb,=20 filling the float bowl with fuel, and observing the = plugs to=20 see if they leak. It would be a rare condition if you = actually=20 have a leaker. But if the primary plugs leak, the only = permanent solution to the problem is to drill the = plugs out,=20 tap the passages for a #10-32 screw, and install a = =BC=94 long=20 allen-head countersunk screw with some good epoxy into = each of=20 the two passages. I see carbs with the plugs coated = with=20 epoxy: Simply smearing some epoxy onto the well plugs = will not=20 seal them permanently. You have to drill, tap, and = plug them=20 with the epoxied screws if you want the repair to = last. The=20 secondary well plugs can be sealed by using the seal = gasket=20 supplied in all of the Echlin brand carb kits.

Wrong throttle plate gasket
Results in: Poor = idle,=20 erratic idle, ineffective idle mixture screws, = symptoms of a=20 vacuum leak.
Comments: There are several different = designs=20 for the throttle plate gasket, and they do not = interchange.=20 Two common problems occur: The first problem was = addressed in=20 a GM Service Bulletin around 1971. There is a = difference in=20 the open area in the gaskets just forward of the = centerline of=20 the primary throttle holes. Some later carbs use a = gasket with=20 a larger open hole in this area. If this gasket is = used on an=20 earlier carb, you will end up with a massive, = undetectable=20 vacuum leak. The other problems with these gaskets = occur due=20 to the idle fuel and vacuum bleed holes not lining up = from one=20 design to the next. Use of the incorrect gasket can = result in=20 blocked idle fuel and blocked vacuum signals. Always = lay the=20 gasket onto the float bowl and onto the throttle plate = to=20 check the hole alignments.

Loose throttle plate
Results in: Erratic idle, = poor idle=20 mixture screw response, off-idle hesitations, symptoms = of a=20 vacuum leak.
Comments: Since the throttle plate = attach=20 screws are located in the bottom of the carb, you = cannot tell=20 that the screws are loose until the carb is removed = from the=20 engine. It is quite common for the screws to be loose, = producing not only a vacuum leak around the base of = the fuel=20 bowl, but violating the seal for the idle fuel = transfer=20 passages. This makes adjustment of the idle mixture = and idle=20 speed almost impossible.

Wrong idle mixture screws
Results in: Poor idle = screw=20 mixture response, poor idle, erratic = idle.
Comments: There=20 have been several styles of idle mixture screws used = in the=20 Q-Jets over the years. The screws differ in the taper = of their=20 tips: Some screws have a steep taper, while others are = very=20 long and slender. Commercial rebuilders typically = remove the=20 nice factory screws and install aftermarket = one-size-fits-all=20 steep-taper screws. These steep-taper screws often do = not work=20 at all in many Q-Jets. Most of these steep-taper = screws are=20 brass. All factory Q-Jet idle mixture screws are = steel. If you=20 have a set of brass idle mixture screws in your carb, = trash=20 them and find a correct set of factory screws.

Seized/rusted idle mixture screws
Results in: = Adjustment=20 of idle mixture not possible.
Comments: A lot of = the cars=20 used in the Midwestern and Coastal States have severe=20 corrosion problems, as we know. The steel mixture = screws in=20 the aluminum throttle plate promote dissimilar metals=20 corrosion, and can often seize solid into the throttle = plate.=20 Attempts to force them out will usually result in the = screws=20 snapping off in the throttle plate, rendering the carb = useless. To remove rusted and seized mixture screws, = the=20 throttle plate must be removed from the carb, and the = screws=20 must be carefully heated while =93rocking=94 them back = and forth=20 to loosen them up.

Seized/rusted fast idle screw & cam
Results = in:=20 Adjustment of fast idle not possible.
Comments: The = same=20 cars with the rusted and seized idle mixture screws = will quite=20 often also have rusted & seized fast idle screws = and idle=20 cams. Once again, any attempt to force the fast idle = screw=20 will usually result in the screw snapping off in the = fast idle=20 lever. To remove rusted and seized fast idle screws, = the=20 throttle plate must be removed from the carb, and the = screw=20 must be carefully heated while =93rocking=94 it back = and forth to=20 loosen it up. To loosen the cam, the throttle shaft = cam screw=20 must be carefully removed, and the spring & = linkage pieces=20 must be carefully pried loose, cleaned up, and = re-assembled.

Primary throttles adjusted to not open = fully
Results in:=20 Poor throttle response, poor WOT = performance.
Comments: It=20 is amazing how common it is for the throttle linkage = on the=20 carb to be grossly misadjusted. When rebuilding a = carb, always=20 operate the throttle linkage and make sure the primary = throttles open fully. They should open the the exact = vertical=20 position. Anything less will prevent full airflow = through the=20 carb. The position of the blades is adjusted by = bending the=20 throttle stop linkage.

Primary throttles adjusted to open = over-center
Results=20 in: Poor WOT performance.
Comments: Even more = common that=20 throttles that do not open fully are throttles that = have been=20 adjusted to open over-center. I guess people figure = that te=20 car will run faster if you can open the throttle even = more.=20 Fact is, once the throttle blades go over-center, they = are=20 restriction airflow just as bad as a throttle that = does not=20 open fully. Check for an over-center condition anytime = you=20 rebuild you carb, and bend the linkage so that the = throttles=20 stop at the vertical positioon.

Secondary throttles adjusted to not open = fully
Results=20 in: Poor WOT performance.
Comments: The secondary = throttle=20 shaft is actuated by a link off the primary shaft that = hits a=20 lever on the secondary throttle shaft. It is common = for this=20 to be misadjusted so that the secondary throttle = blades do not=20 fully open. Some factory cars & carbs were = intentionally=20 set up to limit secondary throttle opening (like=20 1st-generation 400-powered Firebirds) in order to = limit=20 horsepower for one reason or another. Check for this = whenever=20 the carb is disassembled and adjust it by bending the = contact=20 tang on the primary throttle shaft.

Secondary throttles adjusted to open = over-center
Results=20 in: Bog or hesitation going into the secondaries, poor = WOT=20 performance.
More common that secondaries that do = not open=20 fully are secondaries that open too far. Q-Jet = secondary=20 throttle plates should NOT open to the full vertical = position=20 or beyond. The secondary throttle plates should open = to a=20 position where the angle of the throttle plates points = and=20 aligns towards the lower edge of the secondary airflow = baffle=20 located in the secondary venturi bore. When the = secondary=20 throttle plates are opened beyond this point, = turbulence in=20 the secondary side actually decreases airflow. Also, = if the=20 secondary throttle plates are adjusted to open = over-center,=20 they will, as a result, also open too soon. This will = cause a=20 stumble or hesitation going into the secondaries. = Adjust and=20 align the opening by bending the primary throttle = contact=20 tang.

Secondary throttles not closing =96 not aligned in=20 bores
Results in: Fuel discharging out the = secondary=20 discharge nozzles at idle & cruise, poor idle, = flooding,=20 black smoke, off-idle stumble.
Comments: If the = secondary=20 throttle plates do not fully close, or if they are = misaligned=20 in their bores, engine vacuum will be applied to the = secondary=20 venturi area. With engine vacuum in the veturi area, = and the=20 upper airvalves closed, fuel will be siphoned out of = the=20 secondary discharge nozzles. This will cause a very = rich idle=20 and cruise condition. The problem can be caused by the = secondary throttle linkage being bent/misadjusted, or = by the=20 secondary butterflies being misaligned in the throttle = plate=20 bores.

Secondary throttle linkage springs missing or = incorrectly=20 installed
Results in: Secondary throttles not = closing (see=20 above), secondary throttles inoperative.
Comments: = There is=20 no reason to disassemble and remove the secondary = throttle=20 shafts, throttle plates, and the associated springs = during a=20 rebuild, but some people do it anyway. During = re-assembly,=20 these parts get left out or incorrectly assembled, = resulting=20 in the secondary throttle plates not closing fully or = no=20 longer actuating at all. These problems can be hard to = identify unless you are very familiar with the Q-Jet = or unless=20 you have another carb to compare against.=20

Missing secondary airflow baffle
Results in: = Poor=20 secondary WOT performance, sags or hesitations at=20 WOT.
Comments: The baffle installed inside the = secondary=20 venturi area actually creates the venturi effect = required to=20 discharge the fuel properly out of the secondary = discharge=20 nozzles. Deleting the baffle causes turbulence in the=20 secondary venturies that will completely mess up your=20 secondary metering. Make sure the baffle is correctly = in=20 position. It is frequently missing.

Choke plate misaligned
Results in: Poor = cold-running=20 characteristics, sticking choke, engine stalling when = cold,=20 engine not coming down off fast idle unless gas pedal = is=20 hit.
Comments: If the choke plate is misaligned in = the=20 airhorn, the choke can stick and bind in a part-closed = position. It cam also fail to close completely during = initial=20 cold-start. Check to make sure the plate fits squarely = and=20 tightly in the air horn. If not, crack the two screws = loose=20 and wiggle the plate around until it fits right.

Choke pulloff seized or ruptured
Results in: = Poor=20 cold-run characteristics, flooding when cold, stalling = when=20 cold, poor fast idle control, sag or hesitation going = into the=20 secondaries.
Comments: This is one of the most = common=20 maladies on older Q-Jets. When the pulloff fails, not = only do=20 you loose proper control over the choke, but you also = loose=20 opening rate control over the secondary airvalve. = Always check=20 the pulloff by attaching a long piece of vacuum hose = to it and=20 sucking on it. The pulloff should smoothly retract, = and it=20 should smoothly extend when the suction is released.

Choke pulloff incorrectly adjusted
Results in: = Poor=20 cold-run characteristics, stalling when cold, flooding = when=20 cold, engine won=92t stay running after cold=20 start-up.
Comments: The primary purpose of the = choke=20 pulloff is to crack the choke open just a tad upon = initial=20 cold-start. If the choke is not cracked open, the = engine will=20 flood. If the choke is cracked open to far, the engine = will=20 lean out and stall. When correctly adjusted, the choke = pulloff=20 will open the choke =BC=94 as measured from the = forward lower edge=20 of the choke plate to the airhorn wall.

Fast idle screw incorrectly adjusted
Results in: = Initial=20 cold-startfast idle too high or too low.
Comments: = The fast=20 idle screw is hidden so well that many people don=92t = know it=20 even exists. The screw is located under the choke = linkage on=20 the passenger side of the car. The screw head faces = forward.=20 Fast idle speed should be adjusted to about 1200 rpm = on a cold=20 engine.

Choke linkage/intermediate shaft system incorrectly = assembled or missing pieces
Results in: Inoperable = choke,=20 engine not coming down off fast idle, sticky=20 choke.
Comments: The choke and fast idle linkage on = a Q-Jet=20 can be a mystery of odd parts once the carb is fully=20 disassembled. It is easy to get some of the pieces = incorrectly=20 assembled or installed in a bind. When this happens, = the choke=20 system will not operate properly. Best to take a look = at=20 another carb and do a little comparison if you=92re = not=20 intimately familiar with the linkage system.

Broken choke housing
Results in: Poor choke = performance,=20 inoperable choke, vacuum leak.
Comments: The 1975 = and newer=20 Q-Jets use a cast aluminum choke housing for either a = hot air=20 choke or for an electric choke. Many carb kits contain = new=20 choke hosing screws, and these screws are often too = big fr the=20 intended application. Installation of the aftermarket = screws=20 will crack the choke housing, and can make it = impossible to=20 properly adjust the choke cover. The hot air chokes = have a=20 vacuum source from the inside of the choke cover to = draw hot=20 air through the choke system. If the housing is = cracked from=20 the oversized screws, and the choke cover is not = tightly=20 installed, the vacuum source will not pull the hot air = through=20 the system properly, and the choke will remain = =93on=94 too long.=20 Broken housings can be welded.=20

Missing choke intermediate shaft seals
Results = in:=20 Sticky choke operation due to dirt = contamination.
Comments:=20 The 1975 and newer Q-Jets use two shaft seals on the = choke=20 intermediate shaft: One seal is installed inside the = choke=20 housing, and the other seal is installed in the carb = float=20 bowl where the shaft goes through the side of the = bowl.=20 Failure to install the seals can result in a sticky = choke=20 system.

Missing secondary lockout lever
Results in: = Bogging, sag=20 or stumble when going to WOT with a cold engine. = Engine damage=20 from going to WOT on a cold engine.
Comments: The = secondary=20 lockout lever, located on the passenger side of the = carb just=20 forward of the secondary throttle shaft, is intended = to=20 prevent the secondaries from opening when the engine = is cold.=20 Placing the engine under maximum load before reaching = normal=20 operating temperature can result in engine damage. The = lever=20 is retracted by the choke linkage as the choke opens = up. Many=20 people are afraid that the lockout lever is preventing = the=20 secondaries from opening, so they remove the lever. = This is=20 fine on a racecar, but not advisable on a street car. = Make=20 sure your choke is operating, and make sure the lever = is=20 adjusted correctly to perform its intended function. = When=20 properly adjusted it will retract when the engine has = warmed=20 up, and the secondaries will function as intended.

Incorrectly adjusted secondary lockout = lever
Results in:=20 Inoperable secondaries.
Comments: It is possible to = have=20 the lockout lever and the secondary throttle shaft pin = adjusted so that the secondary throttles remain locked = out=20 even after engine warm-up. Check the lockout lever = once the=20 choke is wide open and assure that the lever does not=20 interfere with throttle opening.

Missing idle vent parts
Results in: Dirt & = debris=20 entering the float bowl.
Comments: The early Q-Jets = use an=20 idle vent valve on the forward, upper part of the = carb. The=20 idle vent valve consists of two stainless steel = =93reed=94 pieces,=20 a rubber seal, an actuation rod to the accelerator = pump lever=20 arm, and a sheet metal =93doghouse=94 to cover all the = parts. Over=20 the years, many carbs have come up missing some or all = of=20 these parts. This not only results in a carb that = looks=20 incorrect and incomplete, but the resulting hole in = the top of=20 the carb is a perfect source for contamination of the = carb=20 float bowl.

Incorrectly adjusted idle vent
Results in: = Engine=20 stalling/flooding when hot idling.
Comments: The = idle vent=20 valve is to be adjusted so that the vent is cracked = open when=20 the throttle is at idle, and it should close when the = throttle=20 is moved off-idle. If the vent does not open at all at = idle,=20 the engine may display poor hot idle characteristics = and=20 stalling when hot. If the valve is adjusted so it = never closes=20 at cruise, dirt and debris can enter the float bowl.

Wrong accelerator pump linkage installed
Results = in:=20 Off-idle hesitations, stumbles, flat spot when=20 accelerating.
Comments: Different model Q-Jets use=20 different length accelerator pump actuation rods. Many = of=20 these carbs have been pieced together by rebuilders = using=20 various different parts. If the incorrect pump rod has = been=20 installed, the accel pump may be inoperable for the = initial=20 part of its travel, or the pump may bottom out in the = pump=20 bore too early in the throttle travel. Poor throttle = response=20 and/or hesitations will result.

Wrong accelerator pump installed
Results in: = Off-idle=20 hesitations, stumbles, flat spot when=20 accelerating.
Comments: Just like the pump = actuation rod,=20 different Q-Jet models use different length = accelerator pumps.=20 Use of an incorrect length pump will change the = geometry of=20 the accelerator pump linkage, and can result in an = inadequate=20 or delayed pump shot. After rebuilding a carb, always = visually=20 inspect the function of the accelerator pump to assure = that=20 the pump is discharging fuel into the primary venturis = upon=20 the slightest movement of the throttle (do this with = the carb=20 primed and the engine off).

_______

Lars in Denver
'85 Coupe, no = MAF=20 screen, K&N, Energy Suspension, Bilstein, glass = top,=20 200,000 miles & daily driven... hard.
'71 GTO = Judge 455=20 H.O. 4-spd (12.6 on slicks at sea level)
'68 GTO = Convert=20 455 4-spd - the CorvetteForum Q-Jet Testbed
'74 Ram = Air=20 Formula 455
'80 Ford Pinto (with factory 2-tone = paint it's=20 a collector!)

Xracer
Senior=20 Member

1438 posts [100%]
Rochester = NY

Re: = Q-Jet Problems=20 and Tips (lars)

6:11=20 PM 11/11/2002

Holy Smokes Batman! I will be = printing this=20 out.

Joe
_______

Click here for my Corvette **FOR = SALE**=20 Web Page=20

Click here to E-Mail Me.=20

Proud Member of the The=20 Rochester Corvette Club

silvervetteman
Senior Member

2105 posts [100%]
red light city = of=20 Orlando Floriduh

Re: = Q-Jet Problems=20 and Tips (lars)

6:13=20 PM 11/11/2002

Hi Lars... Just an little note... = your=20 statement.. "Cut Power Piston Lower Stop = Pin
Results in:=20 Hesitations, stumbles, poor idle, surging at cruise,=20 ineffective idle mixture screws, hot = running.
Comments:=20 Many (not all) Q-Jets have a lower stop pin in the = power=20 piston. This pin rests against a cam in the throttle = plate,=20 and determines the lowest (leanest) position for the = power=20 piston. Cutting this pin results in the primary = metering rods=20 seating too deeply into the main jets, severely = restricting=20 fuel flow. Again, there must have been an article = published at=20 some time telling people to do this".... Every Q-jet = rebuilt=20 by holley has this done to it. Terrible throttle = response at=20 anything other than WOT... Go figure. =
_______

69=20 LeMans blue coupe/brite blue int.
427/390 Matching=20 #
M20, PS, PB, AC, PW,Very Original,Daily=20 driver

JB
Senior=20 Member

1381 posts [100%]
Somewhere in = Texas=20

Re: = Q-Jet Problems=20 and Tips (silvervetteman)

7:20=20 PM 11/11/2002

What silvervetteman said. When = he told me=20 this I popped the top on my Holley built qjet & = sure=20 enough it had been clipped off. Replaced it with a = piston from=20 a donor carb and instantly cured my driveability = problem.

No qjets had brass floats? Dang. Looks like I'm = going to be=20 popping the top off my carb again and replacing the = brass=20 float Holley put in there with the right one. Holley = really=20 should stick to their own carbs!

JB
_______

1969 Monza Red Roadster, = 427/390 L-36,=20 4-speed, A/C.
Original radio (it works!), original = spare=20 tire, 3rd owner.

'79ProwlerOrange
Senior Member

1730 posts [100%]
Lifes a = Garden... dig it=20

Re: = Q-Jet Problems=20 and Tips (silvervetteman)

7:43=20 PM 11/11/2002

That is the longest post ive = ever seen!=20 ill be printing that out too. =

also i call you some time this week to see about = the CCC=20
_______

=20

Engine: 347 brake horsepower.
9.99:1 comp. = ratio,=20 Forged Eagle pistons-Rods, forged crank, shaved heads, = overbored=3D4.030, 327/350 horse cam, re-jetted = Q-jet.

The '79 is for sale! im selling it to get=20 StingrayRacing's '72, if he sells before im able to = buy, the=20 '79 is getting a 427BB & ROD 6-Speed!!! (within 10 = years=20 )

American Boy
Senior=20 Member

249 posts [100%]
Quebec =

Re: = Q-Jet Problems=20 and Tips (JB)

7:56=20 PM 11/11/2002

Great info as usual. With all your info, I became = the Q-jet=20 guru of our Qu=E9bec Corvette club. Thanks.

I was missing the spec on the choke pull-off = setting,=20 should crack open to 1/4". I'll check that one since = on cold=20 start, it has a tendency to stall the first time I = start it.=20

D'Oh...my car is in storage for the winter... I'll check it later.

Stephan
_______

1980 Stock L48, 186 rwhp, = Automatic
Fresh=20 paint and running great.

MNJack
Senior=20 Member

8142 posts [100%]
Summit, NJ = NJ

Re: = Q-Jet Problems=20 and Tips ('79ProwlerOrange)

7:57=20 PM 11/11/2002

Interesting about the floats! When I = rebuilt my=20 Qjet it ran like crap. I took out the new brass float = and put=20 the old plastic float back in and it ran much better.=20 Unfortunately the fuel inlet was leaking. Have you = ever seen=20 bubba coat the inlet with epoxy thinking he could tap = some new=20 threads into the epoxy? Can I send you an example?? = MJ
_______

68 = International blue=20 roadster
427 L36 4spd white = top
Summit

Big Fish
Senior=20 Member

241 posts [100%]
St. Charles = IL

Re: = Q-Jet Problems=20 and Tips (lars)

8:21=20 PM 11/11/2002

Great article Lars! I hope this gets = saved in=20 the "FAQ" pages. I am saving it just in case, but I am = confident my carb problems have been solved for now. = Thanks=20 for all the great things you do for this forum!
_______

75 coupe, = frame off=20 restoration almost finished or never=20 finished?

69shark
Cruise-In I=20 Veteran
Cruise-In II Veteran

2688 posts [100%]
Granby = CT

Re: = Q-Jet Problems=20 and Tips (lars)

8:27=20 PM 11/11/2002

Lars, is there a tech tip on sealing = up the=20 bottom of the Qjet, I have a slow leak in mine as I = need to=20 spin the engine over alittle after it sits for a week = or so to=20 pump fuel into it. I think this guy from joisey told = me abot=20 this, right Mark . If you have a link or can = recommend a=20 manual or book.
_______

Tom=20 Gaul
Granby, Ct.
1969=20 Corvette Registry

NRA Lifetime Member =
69-Burgundy=20 Conv.
93-Bright Aqua Metalic=20 Conv13.646@103mph
Send Email Here--> = thomas.gaul@cox.net

lars
Senior=20 Member

2588 posts [100%]
Lafayette=20 Colorado

Re: = Q-Jet Problems=20 and Tips (69shark)

8:52=20 PM 11/11/2002

69shark -
The tech tip on sealing = the bottom=20 of the Q-Jets is included in my post above under the = topic=20 heading "Leaking Well Plugs." You need to drill them, = tap=20 them, and epoxy screw-in plugs into the wells if you = want the=20 repair to last. But before you do this, pull the carb = off the=20 engine, fill up the bowl, and take a look at the plugs = for=20 evidence of leakage: I'll bet you they don't leak. The = most=20 common cause for the fuel to drain out of the fuel = bowl on a=20 Q-Jet is a leaky check valve in the fuel pump. This = allows the=20 fuel in the fuel line to leak back through the fuel = pump after=20 engine shutdown, and this will eventually siphon the = fuel out=20 of the float bowl. You can solve this problem in one = of three=20 ways:
1. Install a fuel filter with a checkvalve. = These=20 Q-Jet inlet filters with checkvalves are available = from=20 NAPA.
2. Install a seat that does not have the fuel = slots=20 in its base. There are "solid" seats available that do = not=20 have the slotted fuel inlet holes around the = perimeter. This=20 prevents any fuel below the upper ridge of the seat = from=20 draining back through the fuel inlet in the carb and = keeps the=20 fuel level up after shutdown.
3. Replace the fuel = pump with=20 a good quality pump.

MNJack -
Yeah, I've seen lots of epoxied carbs, = with=20 drilling, tapping and machine work done to the epoxy = repair.=20 Funny how that just doesn't seem to work very well....

Stephan -
When you do the choke adjustment, make = sure=20 the choke is in the fully closed position. You can = even apply=20 a little light finger pressure on the choke = intermediate shaft=20 to simulate the choke closing. When you suck on the = hose to=20 crack the choke open, apply very light finger pressure = to the=20 choke itself to simulate the force of the air on the = lower=20 edge of the choke. With this light force on the choke = (which=20 pushes it towards the "open" position), and the choke = pulloff=20 fully retracted, the gap should be 1/4".

Silver & JB -
Yes, Holley rebuilding is one = of the=20 biggest offenders when it comes to cutting off the = power=20 piston stops. I have no clue why they do this. It = destroys the=20 idle and cruise performance of the carb completely. I = have a=20 whole box full of cut power pistons - I'm gonna' save = 'em=20 someday when I figure out a good fix for=20 'em...
_______

Lars in Denver
'85 Coupe, = no MAF=20 screen, K&N, Energy Suspension, Bilstein, glass = top,=20 200,000 miles & daily driven... hard.
'71 GTO = Judge 455=20 H.O. 4-spd (12.6 on slicks at sea level)
'68 GTO = Convert=20 455 4-spd - the CorvetteForum Q-Jet Testbed
'74 Ram = Air=20 Formula 455
'80 Ford Pinto (with factory 2-tone = paint it's=20 a collector!)

69shark
Cruise-In I=20 Veteran
Cruise-In II Veteran

2688 posts [100%]
Granby = CT

Re: = Q-Jet Problems=20 and Tips (lars)

9:01=20 PM 11/11/2002

Thanks I'll check into that, I'm = replacing the=20 intake and will have the carb off then
_______

Tom=20 Gaul
Granby, Ct.
1969=20 Corvette Registry

NRA Lifetime Member =
69-Burgundy=20 Conv.
93-Bright Aqua Metalic=20 Conv13.646@103mph
Send Email Here--> = thomas.gaul@cox.net

Captain Morgan
Cruise-In III Veteran
Knocked Troy = out of=20 the bracket racing

4449 posts [100%]
Either at = school or at=20 work What time is it

Re: = Q-Jet Problems=20 and Tips (lars)

11:03=20 PM 11/11/2002

Wow. Thank you for the time spent = typing all=20 that up. I have copied and saved it for future = reference, as=20 with all of your papers.

clem zahrobsky
Cruise-In I Veteran
Cruise-In II=20 Veteran

3988 posts [100%]
delmont = pa

Re: = Q-Jet Problems=20 and Tips (lars)

11:34=20 PM 11/11/2002

lars, on big HP,big cubic inch = engines you may=20 need the "windowed" needle seat to pass enought fuel = to keep=20 the bowl full at WOT. also the "windowed" needle seat = cuts=20 down on the air bubbles in the fuel. just my 2 cents = worth.

quote:
69shark -
The tech tip on sealing the bottom of = the=20 Q-Jets is included in my post above under the topic = heading=20 "Leaking Well Plugs." You need to drill them, tap = them, and=20 epoxy screw-in plugs into the wells if you want the = repair=20 to last. But before you do this, pull the carb off = the=20 engine, fill up the bowl, and take a look at the = plugs for=20 evidence of leakage: I'll bet you they don't leak. = The most=20 common cause for the fuel to drain out of the fuel = bowl on a=20 Q-Jet is a leaky check valve in the fuel pump. This = allows=20 the fuel in the fuel line to leak back through the = fuel pump=20 after engine shutdown, and this will eventually = siphon the=20 fuel out of the float bowl. You can solve this = problem in=20 one of three ways:
1. Install a fuel filter with = a=20 checkvalve. These Q-Jet inlet filters with = checkvalves are=20 available from NAPA.
2. Install a seat that does = not have=20 the fuel slots in its base. There are "solid" seats=20 available that do not have the slotted fuel inlet = holes=20 around the perimeter. This prevents any fuel below = the upper=20 ridge of the seat from draining back through the = fuel inlet=20 in the carb and keeps the fuel level up after=20 shutdown.
3. Replace the fuel pump with a good = quality=20 pump.
MNJack -
Yeah, I've seen lots of epoxied = carbs, with=20 drilling, tapping and machine work done to the epoxy = repair.=20 Funny how that just doesn't seem to work very = well....
Stephan -
When you do the choke adjustment, = make sure=20 the choke is in the fully closed position. You can = even=20 apply a little light finger pressure on the choke=20 intermediate shaft to simulate the choke closing. = When you=20 suck on the hose to crack the choke open, apply very = light=20 finger pressure to the choke itself to simulate the = force of=20 the air on the lower edge of the choke. With this = light=20 force on the choke (which pushes it towards the = "open"=20 position), and the choke pulloff fully retracted, = the gap=20 should be 1/4".
Silver & JB -
Yes, Holley rebuilding is = one of the=20 biggest offenders when it comes to cutting off the = power=20 piston stops. I have no clue why they do this. It = destroys=20 the idle and cruise performance of the carb = completely. I=20 have a whole box full of cut power pistons - I'm = gonna' save=20 'em someday when I figure out a good fix for 'em...

_______

a.k.a. MOTORMAN, 2002 = torch=20 red coupe, proud corvette owner since 1959
NCM=20 member#5583
NCM ambassador from Corvette Club Of = Western=20 Pa
9TH-VETT vanity=20 = plate

=BB = Return to C3=20 Corvettes

Forum Jump Audio/Electronics Breathless Performance =20 = C3 Corvettes =20 =20 =20 Corvettes of Houston =20 =20 Kill Stories =20 Mountain - Prairie =20 =20 = Southwest = West Coast Corvettes =20 =