Mine ran like (as you say) "crap" until I took the HPI carb off and replaced it. I wanted to use an OS carb but the base is too big in diameter and I didn't want to machine it down so I took one off a spare SH engine. With the SH carb it now runs much better and cooler. The engine temperatures went from 300 degrees down to about 260 and the last few times out I didn't even have a shutdown that I couldn't imediately restart. For my truck, the carb was the problem, I do not like the HPI 21BB carb, I think it is junk.