To start off, this is an offshoot of another thread I had but wanted to ask a different, general question. The basic question is: If an engine idles great and transitions quickly to mid and full throttle without hesitation, and can sit in any throttle position for unlimited amount of time without loading up or quitting, can it still be too lean at idle to mid throttle and cause the engine to get too hot?

Reason for question: I had a very rich midrange, Idle perfect and full throttle perfect, but midrange too rich (two needle normal carb). I cut the low speed needle taper angle to a shallower angle to allow the needle to remain active for more of the throttle motion. This leaned out the rich midrange and the throttle was very responsive, no hesitation, no loading up and would run forever at any throttle position. I had the high end set at 500 rpm below peak, and got considerable vapor mist out of exhaust at full throttle. My concern was that at idle and midrange, there did not seem to be any vapor coming out at all, which lead to my question if it could be too lean. It runs and transitions great however and I would assume if it was too lean it would just die from lack of fuel.

I don't want to over heat the engine, however this engine is very finicky about a rich midrange and will snuff out the glow plug if too rich. Although this is a general question that could be asked about any engine, the actual engine in question is a Magnum 52 xls blue head. They have been known for a touchy low speed needle and a rich midrange.