81' Corvette Idling Problems
Problem: As my 81' Corvette, warms up, the engine electric choke does not seem to drop the engine into normal idle. The problem is intermittent but happens more frequently.
Background: My 81' vette has the standard Chevy 350 with the "Quadrajet E4ME" Carburetor. The car has about 85K miles on it. The carburetor system has worked fine and I have had no need to ever remove it for service. The car is garaged and I do most of the work on car myself. My biggest problem is I don't drive it enough but it is well cared for. I have zero experience on carb issues and would appreciate help and/or direction.
Actions taken: I've confirmed that I'm getting 12.5 volts to the electronic choke. I've applied liberal amounts of carb cleaner to all exposed parts to ensure that dirt and gum are removed. Once the car reaches normal operating temp and the engine fails to fall below approximately 900-1100 rpm, I'll remove the carb air filter cover and observe that the forward barrel butter fly valves are not fully open. I place my thumb on the barrel operating linkage to push the valves open while, at the same time, goosing the engine. The barrels move a few degrees further to max open and the engine drops to a normal 600 rpm idle. Sometimes this corrects the problem and other times, it doesn't. As soon as I accelerate a bit. the barrels fail to fully open and the engine idle remains higher than normal.
I've read the service manual but this carb stuff gets complicated quick and I am hesitant to approach things and make it worse without direction. You folks are great and I thank you in advance for sharing your knowledge with me.
Does that carb have a bi-metal spring in the choke housing?
If it does, over time the metal spring weakens and doesn't completely open the choke. Check to see if there is a spring, if there is, replace it.
That's one of the easier things to check.
The fact that the engine rpms drop when you apply pressure to the butterfly linkage indicates that there is no binding in the idle step linkages.
So as SFRY said you are probably going to need to replace your bi-metal choke. (relatively simple if it has screws holding it on).
Before removing it, mark what position it is set to this will be a good starting point for installation and adjustment. There should be a small notch or groove on top of the choke and reference marks on the body of the housing.
If you need any other assistance let us know.
Replace your Choke Pull-Off. They go bad after some time. I have sold plenty over the years to repair garages. They are vacuum operated to pull the choke open as the engine heats up. Its my bet this is your problem.
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