My engnine is 1999 with 1,600 hrs. Head gasket replaced about 25 hrs ago. Mechanic checked valves and said they were ok. Using 10W30 oil. Engine starts fine, but sometimes it lugs down when going from low to full throttle (not when it's cold). Ususally if you throttle back down and then ease it back up, it will pick up. When the engine is running good, it has great power and outruns my 20 hp Walker's. I have checked both coils and have had the Spark Advance Module checked and all are ok. Plugs are new. My mechanic suggested I check the intake gaskets and the right one was cracked. I also noticed some dirt caked along the edge of this right side of the gasket, but that may just be due to the direction of the air flow. I am going to replace the gasket today when I get the part. Could this cause the described intermittent problem? I thought that maybe the dirt accumulated might block off the leaking gasket, but sometimes a small part of dirt would come off and leave a leak until it filled in. It is so frustrating because the problem is intermittent.