i recently purchased a wright stander 36 in fixed deck 15 hp kawi. bought it, changed the oil n cleaned the air filter, new spark plugs, and new fuel filter. the mower just hit 750 hours and when i turn on the blades the motor boggs down very low and builds up rpm. also when you operate mower with the blades on it seems as if it is struggling to keep them spinning. for example bogges down in thick grass cut @ 2mph max and around turns and up hills, anything that really puts stress on the mower. with blades not running its seems to be fine or maybe just not as noticeable. any one have a similar problem? suggestions?