Hello all,
I have a 1982 GMC C1500 with a 305 that I have been having a lot of trouble getting the idle to be relatively smooth.
The truck has 77000 miles on it, and sat for about 10 years before I bought it. It had the original carburetor in it, but everything on it leaked, it idled poorly, and had an off idle surge. I bought a rebuilt Quadrajet from National Carbontooter. It runs great everywhere except idle. When I first start it cold, the idle starts out audibly lower, and it only pulls about 15-16" of vacuum. Once it warms up, it pulls 20" of vacuum at idle, but it has a random misfire. When it misfires the vacuum only drops down to about 19" momentarily. Sometimes it doesn't misfire at all. Sometimes the idle is very rough and audibly slower (I don't have a tach). My calibrated ear says it does about 800 RPM in park/neutral, but when it is idling rougher it sounds more like 650 RPM in park. When it idles rougher, it seems like the exhaust smells a bit rich. I tried setting the idle mixtures for maximum vacuum, and at about 3 1/2 turns the engine starts to stumble, and around 4 1/2 turns is where it pulls 20".
I have noticed sometimes that after the engine has warmed up, the choke light in the dash doesn't come on with the key on engine off. Don't know if that is normal or if it should always be on with key on engine off. Another thing I noticed is that the vacuum advance has vacuum going to it at idle (if I pinch the line going to it, the engine drops in RPM). It is hooked up correctly according to the emissions diagram on the core support.
In addition to a rebuilt carb, it has a new cap, rotor, coil, plug wires, plugs, PCV valve, and about 30 feet of vacuum lines. I replaced the radiator and thermostat (195F) and doesn't seem to run hot. The EGR valve has been disabled. I've put about 1000 miles on it so far and the problem hasn't really got worse or better. Engine doesn't make any weird noises, other than the misfire, and doesn't burn or leak any oil.
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