GPX 250 will not go into gear.

10 Most Common Transmission Problems

www.transmissionrepaircostguide.com/10-common-transmission-proble...

Ever notice that while driving that the car hesitates or refuses to go into gear? ... For automatic transmissions, you might notice that when shifting into drive or park ....Neutral and park gears no problem, but drive, 1st, 2nd and reverse engages ...

Trans Goes Into Neutral While Driving - Transmission ...

www.transmissionrepaircostguide.com/topic/trans-goes-into-neutral/

Jun 5, 2015 - When I put it in drive, and begin to drive away the transmission will put itself in neutral. When I slow back down, it will go back into gear.

check your neutral switch, it's probably loose or faulty

need to look at internal gear selector, may be bent, or springs damaged

Possible busted clutch??

this can be a problem with the clutch\ side stand switches. Use a multi meter to check the switches work

neutral safety switch light must be on to engage starter,sometimes pulling clutch while in gear will let it start.sounds like switch could need checking.does bike roll free even without the neutral light on,in neutral but no light. or is light out because its still in gear?

have you put the gear linkage back together properly. firstly is the linkage the right way up and the rod allso twists in and out to adjust lever position and may be wound to far out.it should turn by hand once the locking nuts are loose ,adjust bit by bit and that should sort it.

James, let off the gas when shifting, especially in 1st and 2nd gears.

The neutral light should only light between 1st and 2nd gears. There may be a "false neutral" at other places. Wear exacerbates (i love big words) the size of these but they don't hurt anything as long as the bike shifts well.