When you say that you are running it richer, I'm going to assume that you are referring to the high speed needle. If you have richened it up as much as you can and it still runs hot, the first thing that pops into my mind is that the bottom needs to be richened. Fat top and lean bottom = one hot running engine.

You might also want to check and make sure that you don't have any leaks in the pressure line between the fuel tank and exhaust pipe. This will also cause a lean situation.

No offense intended, but do you guys know how to tune a nitro engine? NEVER ever tune the bottom until the top is tuned and only tune when you have the engine up to running temps; something over 200F or so.

What I usually do is to set the bottom rich, so that the vehicle stutters from too much fuel when you take off and then it will clear out. At this point, you can tune the top so that the engine is giving good performance, while still showing a steady flow of smoke. When you have the top end tuned, I usually just tune the bottom so that it will idle for about 5 seconds before loading up.

One thing that you should avoid is tuning by temp. I've had O.S. RG engines that would run great at 275 all day long, but the Novarossis that I've had ran best at around 235. Just tune the engine until it sounds right, but I think that I'm safe in saying that 350 is way too hot and you probably damaged the piston/sleeve and maybe even the bearings or crankshaft.

I'm sorry that I can't articulate it any better than this, but tuning is a skill that you gain through experience.

Just as a start, try opening up the low speed needle by a half a turn and see what happens.