I don't use on board glows on any of my four strokes and they all idle fine. I have a 120 in my geebee it flys great. I did NOT have to add any extra weight at all, I have the throttle servo fixed to the bulkhead under the engine, I like my throttle servos in the cowel you get a much better positive linkage and the fuel residule does not do them any harm. I have a plane where the same servo has been fixed to the side of the engine mount for ten years. The standard four cell RX pack is under the tank and the CG is where suggested on the instructions.
Regards
Paul