Expert: Brad Sears - 6/4/2009

Question
QUESTION: Hi, Im in the process of restoring my 68 Buick but i ran into a problem with the engine. The engine runs rough, it sounds like it has a misfire or a (stumble). I was looking on your site and i seen that you had already come across this problem, but i did everything you said and it didn't help. The short cut is http://en.allexperts.com/q/Classic-Antique-Car-2542/2008/9/68-Buick-350-running-. The stumble seems to be random, and it lessons as the engine heats up but doesn't go away. I checked the  distributor shaft for wobble there was no wobble. I even tried loosening the distributor and turning it. That just made the stumble worse each way i turned it. I also tried taking the engine up to about 2500 rpm and disconnecting the vacuum line. It made no difference in how the engine ran except when i revved the engine up it would spudder a little. The stuttering is still there either way. I tried adjusting the carburetor because the spark plugs were a little black, but the stutter didn't change. I sure hope that you can help me because I'm lost.

ANSWER: Ok, lets get a little more history here. What work has been done on the engine in the restoration process? Has it been rebuilt? have gaskets been changed? Is all the emissions stuff in place or has it been removed? Let me know.
Brad

---------- FOLLOW-UP ----------

QUESTION: The only thing that i have done to the engine is replace all the hoses and belts, but it was rebuild around 1985. I don't know what was done because I've only had it about a year. The only emissions is a blow by hose on the valve cover and no its not in place. Its been redirected under the vehicle and the hole in the air cleaner housing plugged. The engine was running extremely rough before i replaced all the hoses and belts and tuned the carburetor. Now it runs and idles good. Thats when i noticed what sounded like a random misfire throughout both banks. I also adjusted the valves because there was some valve noise but that didn't seem to affect the misfire.

Answer
The first thing that I would do to that engine is to run a compression test. Once that is done and the compression numbers are all above 100 PSI per cylinder and they are all near equal, then let me know and we will go from there. If the compression is low there is nothing to do on the outside of the engine to make it all better.
Brad