Quote: Tight guides and seat issues are very common with MP heads.
I noticed you said you were running it hard AND fiddling with the tune. Both of those items COULD have contributed (over-rev or mixture problems). Not pointing fingers just thinking out loud.
Pulling the heads will tell the story. Keep us updated please. Hopefully it's a simple fix for ya'.
I'm sick with the flu so it's going to be couple days before I finish getting the heads off.
