I have a 17 hp briggs OHV on a John Deer mower that is 3-4 years old. Have to move the flywheel past the compression stroke before the starter will turn the engine. Once cranked the engine spits pops runs about half throttle then dies. Noticed that it is blowing back through the air filter. Took the cover off to look at the key in the flywheel. Looks OK but did not take the flywheel off. Any suggestions.