350 - 4 barrel Quadrajet. I have had car 30+ years. Original engine. Not apart except for timing chain at about 200,000. Ran fine.
The car would start up with a twist of the key when cold, or after short off period when warm. If it sat for 15 minutes or so, would have to hold throttle to floor for restart. There was gas odor after sitting too. This went on for several years. Then I started smelling more gas, so I looked under hood and could see gas dripping from between throttle body and middle part of carb near choke, after warm/hot shut-off, and gas in the depression where the accelerator pump rod comes up out of the air horn.
I thought maybe needle valve was worn and letting too much gas in after shut-off
So, I thought it was time to take apart, clean, adjust, new gaskets, and needle valve, which I have done in the past.
Rebuild was without incident. I usually put idle screws to same number of turns they were before, about 2 out, and leave idle speed adjustment alone.
Put carb back on. Air cleaner, vacuum hose going to it, and pipe from valve cover to air cleaner off for all of this. Turned key to start, cranked a bit, then started up and ran smoothly. It reached normal operating temp.
Turned on and off a few times while I checked hoses and connections. Ran fine, though slow idle was too fast.
Then I shut off and turned back on and it ran really rough and was idling so slow I could see the fan and balancer turning. Sound at tail pipe was rough too, putt putt, and some black smoke. Turned off, then re-started. Had to floor throttle to restart and good bit of smoke on restart.
Let it run some (about 10 - 15 min) and stayed running rough.
Came in the house to check troubleshooting to see what it might be.
Went back outside, started up, and it ran fine again, though a bit of rougher idle than typical, but nothing like how rough it was earlier. No black smoke. No adjustments to carb were made at all during any of this, so it is doing these changes on its own.
There is no sign of leaking gas, accel pump rod area dry. On shut off, there is not "smoke" (vaporized gas) coming out of carb. Only sign of gasoline is the air horn gasket is wet in the accelerator pump area. All gaskets were put on carb without gasket cement.
Went back out again to start up. Started up and ran ok, but still a little rough.
My 150' driveway is on an incline, so I let it roll to the bottom and drive up to check acceleration and smoothness. A little rough when first hit the gas but smooths out.
All the above occurred over about 2 hours.
What do you think is going on?
Monday, April 30th, 2012 AT 9:27 PM