I heard that Pontiacs are hard on timing belts. My 69 400 runs strong when cold, but once it warms up. it frequently misses, stumbles or runs rough when you get on it. I replaced the coil, plugs and wires. The distributor has a Mallory Unilite module installed. Can this problem be due to a timing belt?
Actually, the engine has a brand new Holley carb. It may not be set up perfectly, but it should close and not have any leaks. Based on this info, any other ideas?
My 389 runs better when it's cold, too. When it's warmed up it runs more sluggish. When the engine is hot, you're sucking in hot, less dense air from under the hood to burn. Maybe the carb does need tweaking so it's got the right mixture for when it's running at temperature. What we really need is Ram Air to bring in nice cool outside air into the engine.
With your car is warmed up and running take a flash light and look down the bores. You should not see any gas dripping. It has been my experience that every "new" carb needed a fresh rebuild as in every one dripped.. I also could never get a Holley to work worth a flip on my Bird. If you don't have a flooding problem then you most likely need to tweak the carb for your application..power valve jets and such.
Look also for a vacuum leak. Sometimes the expanding parts - especially the intake to head joints - can fit fine when cold but open ever so slightly when hot.
