Last fall he raced, his only race of the year, the box scraper mistake on a whoop left 12" lip on the face of it he hit it with the right front and flipped over the bars and and the quad went end for end twice. He got back on too finish but complained the quad would shake at higher speeds and it wanted to pull really hard. Looked at the following day but din't see anything tweeked, but still says it shakes and pulls.
What am I missing? I know very little about quads.

Ater writing this I noticed I didn't give the specs of what he has,,,,, dummy. 2006 single A-arm DRR 50cc quad. All stock. It works very good for what we need and he loves it.