Problem with Mighty Demon 750

If you are SURE that it's actually 10.5 and not just 10.5 pistons, then the timing might be close. You can try bumping it up around 20 initial but keep the total around 34 all in by 2500 and see how it does. Remember, just because you bought "10.5" pistons means nothing. It all depends on many other factors. Chamber volume, gasket thickness, deck height........If you have not verified the compression by measuring, you could be miles off.