I know the OP got his engine running better, but I figured I'd offer my worthless two cents. Enya 3 plugs work fantastic in 4-stroke engines as well. I've used Fox idle bar hot plugs too with stellar results. Both the Fox idle bar and Enya 3 consistently ran better and gave better idle quality than an OS F plug though it seems the OP's engine won't accept the longer extended reach 4-stroke plugs anyway.