A couple of possibilities, do you have a velocity stack? if not then the air flow over the carb with the cowl on may be too turbulent, the other thing is you may need to make a baffle to direct the in coming air though the fins and not around them, it will keep your engine in check as far as temp goes. The "how to " is on rcs web site. My G-45 in my pitts rus at 189 degrees with the cowl on and I put a velocity stack on that protrudes to the outside of the cowl. Pic's are worth a thousand words, so here they are.