Take the valve cover off and check the valves for the right tappet or gap. While that is apart make sure the head bolts are tight and then put the valve cover back on and if you have a new gasket use it too. You want to make sure all the bolts are tight on that engine and not to have any air leaks at all any where. Just to try it if you can, get a gallon of Morgans Coolpower 30% heli and run through it. As much as you have worked on the regulator area you should have it right. Just start with it flush with the housing and 2.5 to 3 turns out on the main needle and start it again. Let the engine run at a fast idel and get it warm, then slowly start advancing the throttle little by little then listen to it. Try to here how it sound just before it quits. If it sounds like it predetonating then lower the throttle and open the main needle about a half turn then start raising the throttle again. You may have done all this and I'm just typing then. I hope I have helped and keep us posted. I forgot, clean the valve cover bolts good and use good blue loc-tite on them. Make sure you have no air leaks. This thing has go to run

Larry