I have a 2005 yfz 450 that just grunts when you try to start.I have already upgraded the battery and replaced the starter it will run when bump started and it runs really strong we upgraded the battery to the ya10s cbr battery. when we changed the battery it started right up but when my son stalled it it would only grunt.like it has too much compression or the starter was bad.I have tried jumping the selonoid but it does the same thing.