Lawn Boy; I'll try all that and post results. I've run this motor before I got it and it ran/runs like new. The guy made one pass down his drive and turned around and it started backfiring and lost all power but doesn't quit. I thought water in the fuel first but none, wondered about sticking points but they weren't burnt so I filed them and regapped them. Magneto isn't loose so timing should not have been affected. Plug looks good but you know what happens when you assume! I'll change it. Swapped the carb for another used one and it runs exactly the same - warms up smooth as can be, responds perfectly to both low and high speed adjustments (I know, should only adjust when warm but, I'd just put the carb on and didn't want it running lean) then starts belching fire and back firing through the carb so I assumed both carbs are good. Makes me wonder about the valves. Someone at my work mentioned the governor could be worn out but it is functioning fine.
Joker; Good compression and no smoke. I'll throw my compression tester on though when I pull the plug cuz it only takes a second and I won't rule anything out when I obviously don't know either!
WrenchDad & Phil I think I responded to you in there as well, Thank You!
Heater is on and I'm headed out. Thanks again all! :thumbsup::biggrin: