erik, if it stalls when when you drop the idle back down after starting it, it could be tuning, or it could be either the plug. As for a leaky head 'causing it to run hot, that would be because you're adding un-wanted air into the air fuel mixture (air you can't control) which makes it run too lean to compensate for...As the other posts say about tuning, Lean=hot, and Rich=cool....