I agree with Av8tor1977 and Dr Honda, regarding the safe positioning of items relative to the ingnition components...and the use of the throttle trim to kill the engine, along with the stock grounding switch. If you want a similar setup to what you have, for redundancy, use a standard size servo, and operate the choke on the engine. Flip your gear switch to choke your engine. This is cool for starting it up, and if needed, you flip that switch on a warm engine and your engine stops, immediately.

Chad