Hi Jeff,
Not sure what the difference is on as you say a real PT 24 engine is unless they played with the jetting and compression. I have swapped around several of my motors here and they all do this kickback carry on, bizare, just getting me angry because I can't understand it. I have tried with loose belts,tight belts every combination I can think of. I now have this one hopefully working reasonably well by swapping a few decomps in and it seemed better. Will test it again today and see how it goes. I can't be the only one having this issue with these. One part of me says don't ever pick up another one and the other part of me says to get more and see if I can come up with a fix.