I was going through a couple of boxes of plugs a year, and I know how to get it warmed up. I switched to chanpion powersports plugs, ang didn't pull the plugs again until I desided to clean the valves several rides later. try these plugs!
as to why I was fowling plugs, it turned out to be burn't pistons, plug fowling and hard starting are symptoms. I had no real noticable power loss. I think the sled was like that for years, and I never knew until stuck my head in the belly pan and looked up throughthe exhaust ports.
try the plugs and get a good look at you pistons when you do a preseason valve cleaning.