RE: P-51 Mustang PTS RTF Engine
There is a huge thread about this plane in the ARF and RTF section. Try posting your question there as there are a lot of guys with experience with that plane. There are several modifications that are being recomended also in that thread. If you have the RTF version it is actually a .45 size engine not a .40. This is a good engine, very reliable. Look at the low speed needle, it has a limiting collar on it, blue in color. It has the tendacy to "walk" when moving the throttle. This might be your problem with it running. The collar hits the cowl and changes the settings. The collar is easily removed. Anyways check the other thread out for a ton of info on your plane.
Layne