i have a 1986 fourtrax trx 200sx semi auto.. i was jamming through the gears and when i went to slow down and downshift, i noticed that it would not shift into lower gears.. when i was stopped, i tried shifting up or down and nothing... it wont shift up or down and is stuck in about 4th or 5th gear not sure which one but think its in 4th.. what should i do to fix this

 

First check to make sure the foot shift lever is nice and tight. Might have come loose.
Check your oil level also. Trans and engine both use same oil.
And this may sound odd, but check to make sure all bolts on right side (while sitting on it) clutch cover are tight. The shifter arm goes all the way thru the case and is held in place by that clutch cover. A little extra play and the little gear (looks like a 6 or 7 sided star) and lever won't connect with each other.
If all that doesnt help, start by removing the right side clutch cover and check the "little gear and lever" to make sure that is atleast working correctly. Just be careful pulling the cover, some of the pieces and a shaft or 2 are held in place by the cover. Some of the spings attached are a real @#$$^% to get back in right.

 

so its prob just about the same set up as the trx 125 fourtrax? i got one of those for my daughter and had to put sub-trans gears in it as they were missing when i bought it..

 

I only know how it works and how to put it back together from when I dropped the timing chain in while rebuilding my 200sx. When I pulled my cover off the sub lever and reverse shifter shaft came off with the cover. The spring on the reverse shaft was the toughest part to get back in. Not much room to fit any tools there.

Not sure about the trx 125 unfortunatly. But if you've been that far into that bike, I imagine this will be very similar. Theres a couple items (clutch lifter plate and ball retainer) I had to add a glob of grease on to hold them in place while I massaged the cover back on.
I didn't have a repair manual to do this so it shouldn't be too tough. Just keep an eye on everything as it comes apart and make sure to get a new gasket ahead of time.

 

I would check the gearshift arm and the gearshift plate ..

================================================== ==============================================

 

is this on the left side? and would this keep it from wanting to up shift or down shift? i was hopeing something simple, shift drums and clutch ahhh!! dont feel like messing with all that!!

 

Right side while sitting on it.
And yes all those levers and gears have to be in the right place and in good working order to shift up or down. Even a 1/4" of play in the shift spindle could keep it from shifting.
Easy way to check for play is pull foot shifter away from bike and push toward bike. Try pulling away and then shifting up or down.

 

i think i found the problem?? i pulled the right side cover off and found that the oil pump chain was broke.. i called my dealer and he told me that it can cause it not to shift?? dont sound right to me but regaurdless, i need the chain anyways...