I have found the problem: The engine is a single throw crank, and I have the valves going like a double throw crank engine. The exhaust valve is opening on the intake stroke, and the intake valve is opening on the compression stroke! I followed the timing istructions exactly, but apparently they were wrong (the person I bought the engine frome had it timed the same way as me, too.) Hopefully this will fix the problem.

Thanks again for your help, bdtsr! Probably would have taken it apart and put it togeter again with the same problem had you not mentioned the valve sequence.

NJD