While helping others I find the most common problem from engines stalling after a short period of time is they start to lean out as they warm up. Although you did say your running it very rich.
I've helped get a Miss Bud going and the problem with it is it had a very lean LSN from the factor completely effecting the tune.
I have also seen where the feed tube in the tank has a hole in it causing the engine to lean out when the fuel level reaches this hole.

How do you know the engine is overheating?

I have car/plane engines that run 220-320F, which is very normal. On my nitro boat engines I can not get them to exceed 180F. I strongly believe ABC engines should run at 220F if possible.

Just a thought
Ryan