Airframe:
Do this to see if you have a mix issue in the programming. Take the wing off but have it still hooked up the the receiver. Turn everything on but do not start the engine. Make sure you can see your throttle servo. Now move the ailerons with your transmitter back to where the engine died. Look at your throttle servo when you are doing this. If it moves you have a mix set somewhere in the programming. All you need to do to get rid of that is either null it out or do a new setup for a new airplane. If the throttle does not move you got some EMF occuring and sometimes the optical kill switches on spektrum radios do not get along with each other. Also if you have a "Y" connector anywhere in the airplane this is another thing to try and get rid of especially in Spektrum setups. I did not have an issue with a "Y" connector when I was flying with JR but my Spektrum DX7 did not like the "Y" at all. Some may have no issues but just one thing to eliminate. Another thing is to ensure your spark plug boot is firmly seated on the plug. One more thing is to ensure the receiver and the ignition boxes are not close together.
You said you are running one battery. I would recommend you use 2 batteries. One for ignition and one for receiver.
Hope this helps.
Regards
Glenn