Hello everyone, some time ago I bought a used Ultra Sport 60 with a Thunder Tiger 61 engine on the nose at a garage sale. Mind you-- It looks like this engine was sitting for a while, and I had to unstick the carb when I first got it. SO needless to say, it's not a brand-new engine. But anyway, I am at a total loss with this engine. It starts up great, but continuous running anywhere above about 1/2 throttle, the rpms start to drop and it will quickly stall if you keep it there. While I'm not an expert with glow engines, it seems like it's a little hot after it stalls, so the logical explanation is that it is over-heating at the higher speed. This would make sense because I have the high-end needle valve at only about 1 whole turn out. Ordinarily that would be really lean. However, it is spitting out a ton of fuel from the exhaust, so it would seem (to me) to be very rich. I tried switching out glow plugs for the heck of it and even some different props all to no avail. I would appreciate if anyone had any thoughts.

Thanks for your help.

What size propeller are you using on the engine? What fuel are you using, nitro content? Based on what you say, it sounds like the prop is too large for the engine. The glow engines do spew out oil, fuel, etc from the exhaust. So that is normal. You still sound like the engine is too lean and quitting when you try full throttle.

It originally had an 11x6 Master Airscrew scimitar propeller on it. I also tried a 12x8. I am aware that it should spew out some fuel and oil.. it just seems like more than I am used to.I'm using 15% fuel (I think omega, but I'd have to double check).

Needle setting is too lean most likely. What's coming from the exhaust is probably oil. You have to have the needle valve set so rich the engine barely runs to get raw fuel to come from the exhaust. Reset the needle a couple turns richer and lean it down from rich. It's never a good thing to start out lean and work richer.

Sounds rich at the low speed and lean at the high. Your ST should have a long skinny needle valve (high throttle adj) and a short fat needle (low throttle). When you start it go to about 25% throttle and pinch the fuel line with you fingers or hemostats.
If the engine speeds up rpm when you pinch off the fuel line (it is rich at low speed), turn the slow speed adj needle in until when you pinch it you only get a minor speed up in rpm. Keep lowering your throttle as you do this too.
Then go the the high speed, turn it out about 2&1/2 to 3 turns. Set the throttle tx stick as high as you can and it keeps running, pinch and adjust the high speed needle. If you do not get a speed up, then turn your high speed out and repeat the process. Most likely you will end up with the HS needle about 2 turns or more out.
This works for most engines, pinch the line, engine speeds up a lot, it is quite rich. Engine speeds up a little and then wants to die, quickly let go of the pinch and it runs good, YOU got it!