Waking up a 9 year old thread here.
1st thing is check the spring. Even put in a stronger one. Most electric rebuild shops will have a decent selection.
The other thing would be to put some shims between the starter and the bracket. Maybe move it away 1-2mm and see if that helps.
2015 Skidoo Renegade BC 600 Etec
1999 Skidoo Summit X 670 HO (Son's)
1996 Skidoo Touring E 380F (sister's)
1995 Skidoo Summit 583 LQ
1985 Skidoo Tundra 250F
1999 Arctic Cat Jag 340F
1999 Arctic Cat Z 370F (son's) - needs track
1990 Arctic Cat Jag 340F
1982 Arctic Cat Panther 440F