RE: STS Engines
I should also add check the head shims. Make sure you have ALL three there, a silver and 2 coppers.
Basically, when all the possible air leak problems have been addressed but the engine still runs away, their is another air leak that cannot be corrected no matter how much RTV you throw at the engine. Usually, it is the carb at fault. The LSN on STS big blocks is usually the culprit. If you did all the air leak remedies and you still have to richen the LSH to where it is almost falling out, it is for sure at fault.