Small Engines (Lawn Mowers, etc.): vanguard 18hp model 350776 type 1046-e2, head bolts, speed circuits

Question
the engine is running rough worse under a load when i pull the plugs one plug is dry and sooty and the other is wet and blackish, did comp test both about 140psi did a leak down test both passed no leak down changed plugs,coils,cleaned and adjusted carb, set valve clearances, still no change i checked it with a spark tester all ok , i pulled the engine out and checked cam timming it was good, tried running it out of gas to see if it was a fuel bowl height issue still no difference still runs bad then shuts off when out of fuel, ran it with no air filter no difference. Its got me stumped any info or other tests would be greatly appreciated

Answer
Are you sure the carb high speed circuits are clean?  Did you blow compressed air from an air compressor through all the carb orfices when you cleaned the carb.

Is there an intake leak or is the carburetor butterfly shaft wore causing a leak?  Did you check the intake gaskets?  I once had a customer install a gasket on one side that was smaller than the other side...stumped for a long time.  I had another engine that was leaking through the head bolts.  Happened to stumble on the problem using a flashlight while checking some other parts; saw some very small bubbles coming from one of the head bolts on the exhaust side.

Did you torque the head bolts?

Eric