my ignition battery and receiver is located under the fuel tank which is on the CG of 6" (Planes CG is 5.5 inches) my unit is 1/8 dowl pinned in the front former of the plane very near the firewall. my servo battery is located about 2" in front of the 3 rear mounted servos. i use a carbon fiber throttle rod, my servo and ignition switch sit very close to each other. make sure somethiing is not touching around that area along with making sure you wire are not chaffing around were you exit the fuse to get to the spark plug. I have mine wrapped in inner tube from a bike so that they don't chaff. last but not least make sure the ground is still tight on the motor mount area. Only at idle u say?