i have a 96 trail blazer 250

everytime i put it in drive (H), the gear slips back and makes this lound grinding sound in the transmission and the bike doesnt move. Quad has gas, brakes fluid, grease, transmission fluid, and engline oil. Why is this happening? I did try adjusting the idle, but that doesnt work.

 

Just sounds like your shifter linkage needs adjusted, like it isn't going all the way into gear. This is the same type sounds my Boss makes if it doesn't engage all the way.