My buddy has a 2006 mxz rev 1000 yesterday we went for our first ride of the season we where running around 55 to 60 mph and the sled locked up. I know these sleds are know for engine problems any idea would be helpful. Pulled plugs out looked to be burning fine card board brown. The plugs did have very fine alum specks very hard to see them thoe. any thoughts or ideas what this could be will be helpful.