I've had no problems with my Irvine 39 (rappy 30 v2 and zimmerman muffler) running normally it doesn't load up unless it really pushed hard, and has more than enough power for general flying.

Budgy545, what fuel are you running, sounds maybe like you don't have enough nitro/oil. There is a fine line between being too lean or too rich. It definitley overheated if the exhaust solder has melted.