Go with Texasbird's suggestion..

I will add the following.

An engine will not overheat with a rich mixture.
There are exceptions to this:

1) bearings are really shot. You will hear this, and can feel this turning the prop over. If it is bad enough to get the engine hot, it will be obvious.

2) the engine is in cowled-in installation, and there are not adequate or properly placed air inlet and air exit openings

Since you noted that you were new to this, I will assume for a moment that this is not a cowled-in or scale application... and the engine cylinder is out in the breeze.

Ruling out the two above....

If the engine is overheating no matter of the mixture setting, you ARE getting air in the fuel system

Air comes from two sources. Fuel foam, and leaks. You have one, or both happening.

This will cause you all sorts of headaches with transition and everything you described.

Assuming the engine has not been crashed and the crank shaft is not bent....

1) BALANCE THE PROP !! If it is shaking, something is out of balance. Modern engines run smoothly at nearly all power settings. Change the prop, and make sure the new one is balanced.

Shaking WILL cause the fuel to seriously foam in the tank, introducing air into the fuel which will cause the engine to run lean, no matter what, and it will over heat rapidly.

If the engine runs OK at low speed, sorta ok in mid range, and will not run at full throttle in the air... it is highly likely the installation is generating foam in the fuel.

Balance the prop. Make sure the tank is isolated from the fuselage structure - wrap it with foam. (see item 3 while you are at it)

2) Check the fuel lines running from the tank to the engine. If you have a remote needle (see 2a) replace the tube from the needle to the carb. Make sure the vent line and feed line are flowing freely and are not kinked. Make sure the pressure/vent line is properly connected to the muffler pressure fitting, and that fitting is not clogged. You should be able to GENTLY blow into the vent line, and cause fuel to easily flow out of the feed line.

2a) Note if you see clear fuel going to the needle, but bubbles in the remote needle to carb fuel line, there is a possiblility the needle valve o-rings are not properly sealing, allowing air into the system.

3) Remove the fuel tank. Check the clunk & pick-up line inside. Clunks and tubes often fall off, or the tube ends up with a cut where it mates with the metal tube. This is very common and can drive you nuts! Make sure the clunk is not stuck against the back of the tank. It should move freely at all times.

4) Pull the engine from the airplane. Check ALL of the bolts on the engine. Yes, on a 2 stroke engine, the crank case is part of the fuel system. The bolts and covers are potential sources for air leaks. Make sure the crankcase/backplate bolts are tight... the head bolts... everything. Don't go nuts an strip them, just make sure they are snug. A leaking backplate or loose cylinder head can cause some of the problems you noted.

5) Make sure the carb is properly installed. This is a potential source of an air leak. On the TT61 I believe there is an O-ring seal at the carb/crankcase interface. Make sure the carb is pushed down against the seal, and the retainer is snug.

6) Change the glow plug. Might be ok, but it ever hurts to try. Make sure the glow plug is tight (Again, don't go nuts here) The OS8 is a great plug for the engine. K&B plugs, Merlin plugs, Tower plugs... all suitable for that engine. There are few that are not good. However, on rare occations glow plugs develop leaks in the center seal, or could leak around the crush gasket. Does not hurt to check if nothing else above worked.

Often times people have written to me with symptoms where the engine runs well on the ground, but the needle goes away in the air... and the engine gets lean and hot. That is a classic symptom of foam in the fuel. You may not even see bubbles in the fuel supply line on the ground, but when the engine unloads a bit in the air, it hits the right note to foam the fuel.

I hope this is helpful

Bob Brassell

Jett Engineering
Engine Mfg Support Forum