Try cleaning the jets.. Make sure air flow is good (only because you mentioned filters) make sure when adjusting your air fuel screw bottom it out and start turning from there. Is it sending any fuel out of the over flow on either side?. Also plugs. Update would be cool! Mine was a 20 kick starter and leaked fuel out the over flow after shut down until i took the carbs apart and found that the jet was clogged to a pin hole size. Cleaned and now 1 kick, maybe 2 but rarely.