Got an ole Tecumseh (ohv155 204508d h) Have tried everything I can think of except a coil and still it backfires through the carb and sounds like in the muffler as well. Mostly at lower speeds. At full throttle it seems like its misfiring. While running I can spray carb clean in the intake and it will rev and run smooth. Key ways good, valves lapped and adjusted propper, new carb, new spark plug. Ive had the motor for years but never heard it run. The original carb was so bad it had to be replaced. Cant find a reasonable priced oem so the replacement is aftermarket. Tried drilling the jet with no change. Im sure this has been dealt with elsewhere in the forums but I never see any solutions. Thoughts