I am having a problem with my OS 21RG(X)P engine in my 1/8 buggy when it heats up. It idles really fast. It only happens when it reaches it's full temp after a few laps or so. It's as if something is expanding and allowing air to leak in, leaning the mixture. I've tried turning the idle mixture screw until it's very rich, and I mean "very rich" but it still does it after a lap or two of the track. I mostly use Blue Thunder 20% nitro fuel which I've been lead to believe has enough oil content for this engine, (18%). When I adjust the idle speed screw I can get the idle speed down a little but if I go too far then I close the barrel altogether and it dies. When I find a happy medium if the engine is allowed to cool for even just a minute then the idle speed is too low and I have to adjust it back again. The engine goes fine when the buggy is actually going which seems to indicate there is nothing wrong with the high speed needle and it starts ok. The compression feels ok even though I don't have any accurate way of testing it. I've taken out the piston and liner and they look fine. No scratches or pits. I'm no expert on this matter though. I've also taken out the needles in the carb and made sure they were clean. Sometimes just before the engine reaches it's full running temp, if I rev the throttle, the engine will rev but when it's returning to idle it will rev high for just a sec and then return to a normal idle. I've also looked at my throttle linkage to make sure it's returning to where it should and it seems fine. I've tried different glow plugs from medium to cold but nothing seems to make a difference. This has only been happening lately and I hope you can help me. If you need any more details I will pass them on. Your help would be greatly appreciated.