I tried the glow plug wsher, and it's not enough. The head shims actually go between the button head and the cylinder. I've had a couple of Force .26's, and they both needed a couple of head shims to get them to run right, even with 20% nitro. They actually made decent power after that too. The timing is too far advanced in these engines. Or they just simply are building them with too much compression. Same difference. I switched to an MC59 plug too. This made for less flameout trouble.