I have an LX277aws with the FH500V 2-cyl engine. I've already syphoned out the old gas and replaced with fresh 93 octane. The fuel filter is new, the air filter is new, the carb has been inspected and cleaned. The spark plugs have been replaced and gapped to .040 per JD spec. The engine seems to idle ok but as the RPM increase there is misfiring. Could a coil be going bad causing the higher RPM misfire? I've already pulled each plug individually while it's running to see if it dies, and each cylinder is firing as the engine stays running. Any suggestions to narrow this down without throwing parts at it?