I just baught a used rc car (Caster zx) with a .21 Go engine. The first time I fired the engine up it ran good and revved out great but I did not drive the car on the ground. The next day I started the car and drove it and everything worked great (engine temp about 230-240), lots of power! I stopped the engine and refueled, then ran it again and everything was good, but after about one minute the engine died when I opened the throttle. So I leaned the high speed needle and the engine ran great again. A few hours later I took the car out and ran it again and it started and ran good at low speed but died when I opened the throttle, so I leaned it again and it ran good but then was leaned too far and was running hot (over 300). So I stopped it. I checked the fuel system and everything looks good. Later that day I tried retuning the engine but no matter what I did this time the engine stalls when I open the throttle to full. What could be doing this? It ran GREAT the first two times I ran the car, then it changed!
Also the idle has started to quiver a bit now, but not bad though.

Could it be the glow plug?? Engine runs at idle and at low speeds good but once the throttle is open towards full it stalls.

If the engine idles well the plug is fine. If the thing stalls upon opening the throttle, lean in the high speed needle 1/4 turn, it should improve. You will find that you think the engine is running fast, but in reality it has more adjustment to go on the HSN. you will be surprised at how it will run. make sure that there is good smoke coming from the exhaust, with no excess unburned fuel coming out.

When I lean the needle 1/8 it runs at full throttle VERY hot (over 300) and loose power. If I richen the needle 1/8 it immediately dies at full throttle. End result, at full throttle it wants to run hot to the point of damage, or not run at all. I thought it might be the glow plug because heat is keeping it going and cool fuel seams to kill it.

Just thought I'd post this for anyone else who might be having this problem, today I bought a new turbo glow plug and tryed it in the engine, everything is great now! Engine runs at full throttle now, even if its running very rich and smokey it will not die!
In the past I've found that glow plug usually work or don't work, so I was unsure if it was the plug causing the problem. I think that the plug was just running too cool and the engine had to run lean and hot to keep the plug glowing. Just a bit more fuel and it put the glow out, just like throwing 20 gallons of gas on a small birthday candle all at once.