Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Rebuilt Carb-Still Gassy
batsong:
Hi. I've just rebuilt carb 17059212. The book was great, and now the carb is idling, cruising and performing much better. The only problem is that while improved, the gassiness out the tail pipe is still present and fuel economy is still bad. I used "recipe #3" from the book. I am working with a 455 with 9.5-1 and a cam with 230 @ 50. The carb is sucking a lot of air and pulling a vacuum tube makes the engine speed up. Covering the choke horn causes the engine to die. The car still has points which is all new, but it will soon be replaced with HEI. Will this help? Any more carb work I could do? Drilling throttle plates maybe? Was is causing this?
Thanks, Gabe
batsong:
I just tried drilling the throttle plates, and it did not help. Still very rich. The lope came back, it's running alot like it did before enlarging the idle passages (no jerkiness at cruise, though). Maybe the efficiency is a little better, but I liked the way it ran before drilling.
Cliff Ruggles:
Drilling the throttle plates is done to lower the throttle angle at idle speed. The carburetor includes an idle bypass system which does essentially the same thing.
When you get time, list the items from the "recipe" and what sizes you made them. This includes:
upper idle airbleed:
lower idle airbleed:
main airbleed(s):
idle bypass air:
mixture screw holes in baseplate:
idle tubes size:
idle downchannel:
main jet:
primary metering rod:
fuel inlet seat diameter:
float setting:
incoming fuel pressure:
You also mentioned that pulling a vacuum hose causes the engine to speed up a bit. Are you able to slow down the engine at idle speed when you turn the mixture screws in?......Cliff
batsong:
Cliff, here is a list of what I have done so far. I realize that I did not drill out the air bypass. I thought that they were already .070. Drilling the throttle plates with a .094 hole seems to have helped with the fuel economy (I'm getting 12 mpg now!), but I liked the way the car ran better before. I left the idle screws the way that they are are because they have never been touched and I would have to cut the throttle plate, and nothing else I have done to the carb seems to have cleared up the richness. In other words, I don't think that I have touched upon the cause of the problem yet. Your book and the resulting mods to the carb helped enormously in other regions, and I am thrilled, but I am thinking the problem may not be in the carb after all. The richness is so excessive (I can smell strong exhaust going down the highway with the windows closed) that I'm thinking that there is something simple that I'm missing. I tried swapping coils, but the new one I bought turned out to be defective, so it's taking a little time to return it and get another. I've got a MSD coming today.
upper idle airbleed: (in airhorn) .059
lower idle airbleed: stock
main airbleed(s): stock
idle bypass air: stock
mixture screw holes in baseplate: stock
idle tubes size: .040
idle downchannel: .059
main jet: .075
primary metering rod: later style rod turned .026 at the tip and .050 at the widest part
fuel inlet seat diameter: .135
float setting: .375
incoming fuel pressure: no gauge yet
batsong:
Just put a gauge on the fuel line. It's bouncing between 4 and 6. Put a cheap regulator on too. I turned it down to 4.5 and even lower but the richness did not go away.
-Gabe
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