1978 Chevrolet Corvette



January, 10, 2009 AT 4:11 PM

Engine Performance problem
1978 Chevy Corvette V8 Two Wheel Drive Automatic 55000 miles

I've have chev corvette with a quad carburator that was rebuilt. I've replaced plugs, wires, and air filter. The car starts, but has black suttie smoke coming from exhaust. I've checked all the plugs, they too have dry, suttie disposits on all of them. The only thing I've changed other than the plugs and the wires has been the carburator. Any ideas way it has this black disposits on the plugs and how to correct it.


5 Answers



January, 11, 2009 AT 12:19 AM

The fuel/air ratio is too rich. Meaning that there is too much fuel entering the motor for the amount of air. If the carbuerator was rebuilt at a shop take the car back to them and havethem adjust it



January, 11, 2009 AT 12:13 PM

How do I do that. I know to adjust the idle first, but how do I adjust the air/fuel ratio.



January, 12, 2009 AT 11:23 AM

Is it a quadrajet?



January, 13, 2009 AT 5:51 PM




January, 14, 2009 AT 1:27 PM

Set the parking brake and block the drive wheels.

Remove the air cleaner to gain access to the carburetor, but keep the vacuum hoses connected.

Run the engine to normal operating temperature with the choke open.

Turn the A/C off.

Disconnect and plug the vacuum advance hose at the distributor.

Check the ignition timing and adjust as necessary.
Using a sharp knife, carefully remove the plastic caps from the idle mixture screws. Use extreme caution to avoid bending the mixture screws.

Lightly seat the screws then back out equally just enough so the engine will run.

Place the automatic transmission in drive or the manual transmission in neutral.

Back out each screw (richen) 1/8 turn at a time until the maximum idle speed is obtained. Then set the idle speed screw to: Standard engine (180 hp) M.T.-800 rpm, A.T.-550 rpm; Optional engine (210 hp) M.T.-900 rpm, A.T. (low altitude) 750 rpm, A.T. (high altitude), 650 rpm.

Turn in each screw (lean) 1/8 turn at a time until the idle reaches the following rpm; Standard engine (180 hp)-M.T.-700 rpm, A.T.-500 rpm. Optional engine (210 hp)-800 rpm, A.T. (low altitude), 600 rpm for A.T., high altitude.

Reset the idle speed to specification.

Reconnect the vacuum hoses and install the air cleaner.

Feedback is appreciated

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