Hello; For some reason, I can't seem to upload pictures today or you'd be looking at my two OS 90's. I use an alligator clip to light up the glow plug. Attached to my flight box. I also have a few Enya four strokes, so it's nothing new to me. I have lost that back cap. A friend of mine who has a little metal lathe, machined a cap out of a dime and fitted it for me, problem solved. The same fellow made a muffler end cap for me whin I lost that on one of my OS 90's. He just turned out the inside of the muffler a little, then turned down the dime to make it an interference fit, then he set it in place and folded the sticking out aluminum around the dime. He used a dime because a washer costs 29 cents now.