1979 L48 Engine problem?

[Ken C.]

I have recently noticed that after a long run and the car is shut off for more than 15 - 20 minutes that on re-start up I have to pump the accelarator to get the car to restart ( normally just jump in turn the key and she fires) and when it fires I blow out plumes of black smoke and once the smoke clears it runs clean again. Is this a carbon build up or something to do with the carb being set too rich? Also it seems that the car is also running very hot at high speeds, but drops to normal leaves at nomal posted speeds (60 - 70 mph). Any ideas on what could cause this problem?

Any help with these problems would be appreciated.

Ken

[Michael W.]

Re: 1979 L48 Engine problem?

when it fires I blow out plumes of black smoke

Well, you must have an interesting laundry bill.

What happens if you just hold the gas pedal to the floor (no pumping) and crank it. What if you pump just once then crank?

I guess cold start is normal. Have you verified choke position?

The plumes of black smoke infer that you have an extremely rich, almost flooded, condition. This can be brought on by the action of repeatedly pumping the gas.

[Michael B.]

Re: 1979 L48 Engine problem?

a few quick things to think about - if overheating at speed maybe timing or (hopefully not) a worn exhaust cam lobe.

At the 79 there are a lot of vacuum controlled components that could be affecting you including EFE and EGR. If EFE does not work right it will leave the heat riser closed and overheat the engine.

Check that the carb butterfly is opening at correct temp but that would not explain overheat, EFE would. Check vacuum hoses for leaks or just replace and recheck.

Good luck.

Michael B.

[Edward J.]

Re: 1979 L48 Engine problem?

Ken, Black Smoke On Start Is A Related Fuel Problem, Choke, Carburetor Could Also Be Dumping Fuel When Shut Down, Which Would Be A Heavy Float Or Float Level Being To High, Anyway First Check That When Engine Is Warmed Up That Choke Butterfly Opens Fully And Stays That Way After Car Is Shut Down For A Least 30 To 45 Minutes. Next If Okay, Check To See If Fuel Is Being Dumped Into Carb. After Shut Down, Look Down The Throat Of Carb. To See If Fuel Is Dripping In.let Me Kow How You Make Out. Hope This Helps, Ed

[Ken C.]

Re: 1979 L48 Engine problem?

Gentleman, I want thank each of you for your input. I learn more everyday via this forum. Anyway, Michael B I have decided to first follow your suggestions and as the car is all orginal and over 30 years old, decided to change all vacuum hoses (noticed one along firewall was breaking) and the EFE as well. Once done will give her a good run and see what happens. If the problem still exists will check out the carb per your suggestion Ed. I hope these steps will eliminate the problem without having to have my mechanic check it out.

I will let you know the outcome. Thanks again guys.

Ken

[Ken C.]

Re: 1979 L48 Engine problem?

a few quick things to think about - if overheating at speed maybe timing or (hopefully not) a worn exhaust cam lobe.

At the 79 there are a lot of vacuum controlled components that could be affecting you including EFE and EGR. If EFE does not work right it will leave the heat riser closed and overheat the engine.

Check that the carb butterfly is opening at correct temp but that would not explain overheat, EFE would. Check vacuum hoses for leaks or just replace and recheck.

Good luck.

Michael B.

Michael it looks like you and Ed were on the right track. Decided to start with the timing and found that it was way out, 6 degrees retarded. Adjusted to correct timing and then adjusted the floats etc. As the car seemed to run better took it out for a good run, 150kmh for 15 minutes and no problem with heating up. Next let her sit for 30 minutes and then fired her up with no problem. Thanks for your suggestions guys it was really appreciated and hope to return the favor someday. Happy Corvetteing

Ken