I have a DEK 15 hp chipper/schredder. I left the gasoline value open during the winter and gasoline leaked into the crankcase. I drained all the oil and flushed the crankcase with new oil to make certain all of the gasoline contaminated oil was removed, and refilled the crankcase. I examined the air filter for cleanliness. I started the engine and it started on the first crank as it normally does. It is always easy to turn over. I used the machine for about 30 minutes and shut it down to move the pile of chips to another part of the yard. When I returned, I tried to start the engine and it was almost impossible to pull the crank at the compression stroke. This has never happened before. I pulled the spark plug thinking the engine had vapor locked. The engine turned over easily. I left the plug out in hopes of drying out the cylinder. I installed the plug and same situation. I checked the intake and exhaust and found no problems. The oil level was a little high so I drained some of the oil to get the level to the bottom of the fill connection. I took the value cover off and pulled the plug and watched the valve movement. The intake and exhaust values moved freely. The values do not appear to be sticking. I installed the spark plug and the same situation. I am baffled. What am I missing and what should I do next?