Quadrajet HELP
Intermediate
Joined: Feb 2005
Posts: 41
Likes: 0
From: Goldendale Washington
When I got my '76 it "ran ok" with an odd pulsation between fast and a slow idle just sit'n there. Once I got it home I tried time after time to dial in that Q-jet to where it'd stop running so dang rich and inconsistant to where the exhaust wouldn't tear up my eyes so bad. In the process I found it had not just one but several vaccume leaks at various points throughout the vacinity of the carb... to include the carb gasket itself. Ultimately, I took the carb off and stripped it as much as I dared and found that there were many assembly screws and nuts that were exceptionally loose that held the carb together. After basic cleaning and retightening then reinstalling the carb on a new gasket and replacing any and all hoses that were leaking air, then resetting the fuel and air set screws to something more acceptable I found a tremendous new life now exibiting from that motor. I'm surprised the dang thing ran at all beforehand.
A quick way to detect for air leaks is cover the exposed carb with a clean rag at idle then spray WD-40 or brake cleaner around any carburetor hose or carb connection to the head itself. A significant idle increase will occur when the spray is sucked into the carb at that leak. It may be possible that someone tuned that Q-Jet of yours like they did on mine, to compensate for vaccume leaks they didn't know (of didn't give a rip about) the thing had. If the leak varied any, say became less for some reason, then immediately the carb would be running excessively rich and sloppy. That's what was happening with mine... I'd get something dialed in that seemed to make things better, then reved the motor once or twice and it'd be back to running crappy again and needing more adjustment one way or another. Up to that point I was getting maybe 10 to 12 mpg. I now get 19 - 21 mpg depending upon terrain and driving habits.
I'd look into vaccume leaks outside and "inside" the carburetor, would be my guess.
A quick way to detect for air leaks is cover the exposed carb with a clean rag at idle then spray WD-40 or brake cleaner around any carburetor hose or carb connection to the head itself. A significant idle increase will occur when the spray is sucked into the carb at that leak. It may be possible that someone tuned that Q-Jet of yours like they did on mine, to compensate for vaccume leaks they didn't know (of didn't give a rip about) the thing had. If the leak varied any, say became less for some reason, then immediately the carb would be running excessively rich and sloppy. That's what was happening with mine... I'd get something dialed in that seemed to make things better, then reved the motor once or twice and it'd be back to running crappy again and needing more adjustment one way or another. Up to that point I was getting maybe 10 to 12 mpg. I now get 19 - 21 mpg depending upon terrain and driving habits.
I'd look into vaccume leaks outside and "inside" the carburetor, would be my guess.
Drifting
Joined: Nov 2002
Posts: 1,665
Likes: 1
From: Ontario
There are a number of great QJet articles here. 
http://wiki.corvettefaq.com/index.php?title=Intake
http://wiki.corvettefaq.com/index.php?title=Tuning
http://wiki.corvettefaq.com/index.php?title=Intake
http://wiki.corvettefaq.com/index.php?title=Tuning
