'72 - LT1 engine runs kinda rough

[Jerome P.]

At low RPM's and driving the engine seems to run a little rough, however at higher RPM's and higher speeds I do not feel or sense the engine is running rough. Any thoughts? The spark plugs have less than 1,500 miles on them, but have been installed for about 2-1/2 to 3 years.

[Christopher K.]

Re: '72 - LT1 engine runs kinda rough

Jerry,
Hard to say without some more info but the most common cause is a Vacuum Leak.
Here's a quick video that sums it up:

http://youtu.be/io2C2YIxgiI

[Anthony F.]

Re: '72 - LT1 engine runs kinda rough

A vacuum Leak is a real possibility.

I experienced a similar issue recently on my 72 LT-1, idle and low-speed roughness but running fine at higher RPM. As it turns out, the accelerator pump diaphragm on my Holley was going bad, so I had the carb rebuilt. The mechanic also discovered some 'dirt/debris' in the fuel bowls (not sure how it got past the filters, but maybe gasket material?). Runs great now. My mechanic said the diaphragm can begin to deteriorate on a Holley after 5 years or so, so it could be carb related.

Also, probably less likely, when my fuel pump went bad about 10 years ago, the symptoms were similar, except the roughness was not 'llittle', it was 'very'.

I believe there are threads on the forum dealing with tracking down C3 vacuum leaks. Also, Dr Rebuild sells an instruction manual on diagnosing vacuum leaks.

Good luck!

[Edward J.]

Re: '72 - LT1 engine runs kinda rough

Chris, Try running the car with the vacuum advance hose un-hooked and vacuum hose plugged . I had a surge @ low rpm with my 63 , It ended up the vacuum advance was Bad would not hold vacuum .