I got this motor from my brother-in-law and cant seem to chase the gremlins away. It will run great for a little while and all of a sudden only run half speed, without my changing anything with the throttle and stalls when changing direction. It also does not want to idle and is difficult to start after stalling out. I have replaced the fuel filter, fuel bowl gasket, spark plugs, fuel tank, fuel lines and tank connection fitting with no improvement. Any suggestions?