engine runs rough

[Dan Smithwick]

My 57 tbird with 312 runs real rough until it warms up . This is something
that has just started to happen . I have a new rebuilt holley carb on it . But
it worked fine for first 5 months . Wondering what else to look for ?
Thanks

 

[paul2748]

Check the timing. Also check the valve lash. - .019 Pull the plugs and make sure all are firing. Plugs have been known to go bad. If the plug wires have not been changed in a long time, they may need replacement.

 

[HeadacheGuy]

Does it still have points? If not check them as well. Dwell variation gets worse until the shaft expands if the gap is too small. Recommend going electronic if you have not already done so. Valve adjustment is important but usually runs worse warm as the valves tighten up as everything expands. Power valve in the Holley may be leaking (new or not) but usually runs crappy warm as well. Is it just at idle or all the way across the board? Also does it erractically run rough or is it rhythmic like a single cylinder miss? Answer to that question narrows the search.

 

[Dan Smithwick]

Thanks for the responses . I think I may have caused my own problem . I
put headers on the car and of course the manifold heat rise valve was removed . I am thinking this is my problem .
Thanks

 

[BudMY]

I have been told that in cars (ANY CARS) with a carburetor it is best to use gasoline without ethanol. The ethanol in today's gas causes carbon buildup in the intake manifold and in the carburetor itself. If you just rebuild the carb it does not solve the problem. I lived with rough running, stalling and hard starting on my 1979 Lincoln for 30 years. The mechanics kept rebuilding the carburetor, which lasted only a few months. After the 4th rebuild did not work I brought the car back to the dealer that did the last work. They finally found extensive carbon build up in the intake manifold. Removing it and cleaning it out has solved the problem. They told me not to use regular gas with ethanol. I have used ethanol free gas for the past year with no problems. I suspect this might apply to most, if not all cars with a carburetor.

 

[paul2748]

In all my years of working on old cars I never heard of such a thing. I can't see why carbon will build up in the intake manifold because there is no combustion going on in there to produce any carbon.

I have used ethanol fuel in all my old cars (4) for years (probably 30 years) and never had any fuel related problems caused by ethanol. All have carbs.

I have been told that in cars (ANY CARS) with a carburetor it is best to use gasoline without ethanol. The ethanol in today's gas causes carbon buildup in the intake manifold and in the carburetor itself. If you just rebuild the carb it does not solve the problem. I lived with rough running, stalling and hard starting on my 1979 Lincoln for 30 years. The mechanics kept rebuilding the carburetor, which lasted only a few months. After the 4th rebuild did not work I brought the car back to the dealer that did the last work. They finally found extensive carbon build up in the intake manifold. Removing it and cleaning it out has solved the problem. They told me not to use regular gas with ethanol. I have used ethanol free gas for the past year with no problems. I suspect this might apply to most, if not all cars with a carburetor.