Alright so we bought the bike for cheap and previous owner said it was stuck in first. Tore it all apart and fixed it. Well we put it together today and it fired up. We did do a brand new harness too that we had to make our own. Yay it fired up. Put it in first and it lurches forward. Like I know there's clutches in it so shouldn't it require some throttle to get going and not just lurch forward? Any help would be greatly appreciated. All gear works fine.

 

If it is like a motorcycle then you need to pull the clutch lever before engaging gear. However many Quads are "semi automatic" these have no clutch lever but a lawnmower style centrifugal clutch for setting off. You stick it it in gear at idle, rev up and the centrifugal takes up the drive. Most likely cause of lurching, with one of these, is idle set too high. If that is OK, there is a one way clutch in the middle of the centrifugal to keep it driving when on the overrun. If that is seized or put back in the wrong way round, you will have it driving all the time.