If you have a timing light here is something you can try. Put a paint mark on the rotating screen of the engine. And then start the engine at idle. Make a note of what position that mark is in with the light and mark it on the blower housing, and do the same with both cylinders. Are the two marks 90 degrees apart. and also if you increase the rpms down the timing flash change in relation to the previous mark on the blower housing. Basically you are testing to make sure that both cylinders are firing at the correct time, and that the spark advance is working.