I have a 1998 ktm 65 sx I just bought it when we test rode it it ran good but we only took it to 3 rd gear then when rode it after getting it home the first time it went into 5th gear it got stuck there and wont downshift now any suggestions on what might be wrong thanks for your time

I would expect it to be in the user manual, links attaghed:

KTM 65 MANUAL KTM PDF Manuals Judd Racing Youth Motocross Parts

KTM 65 SX 2015 Downloads

OWNERS MANUALS CATALOGUES

Lack of gear fluid, worn gear selector or synchro.

I had the same prob with my bike heres what i did.. I took the cluch all apart soaked all the clutch plates in oil. Than i ordered new clutch springs from <Motosport.com.> Than put all back togeather and rebled the clutch and it work like a top.. HOPE THIS HELPS..

Your clutch basket is the link between the engine and transmission. Your kick starter rotates the clutch basket gear, which turns another gear at the engine crank. Remove either the basket or gear at the crank and see if the engine, and the transmission both turn. Sounds like the engine is stuck for some reason. At least you can cut the issue in half.

Thank you for contacting FixYa with your inquiry.
Check out page 11 of the KTM owners manual from this link.
http://dl.owneriq.net/0/023acca0-f8aa-4324-8970-4f4dc4ccad41.pdf
The plug may be hiding behind the brake lever. Also check page 30 of manual on same like for info on the site glass and a good illustration of the Drain Plug.
Oil Recommendation: Remove the filler plug 4 and add 0.30 l gear oil 20W30 (e.g. Motorex Top Speed 4T 15W50). Mount the filler plug and check the engine for leaks.
Hope this helps. Please advise if we can be of more service.
Kind regards,
TF

Had this very same problem with a KX 85 last week! Turned out funnily enough to be the spark plug. So try this first mate. If that dosn't fix it then you have the age old mechanics question "did I do somthing wrong or is it just a coincidence". Start back at your beginning next & re-check your valves.Most of these late model bikes(12000-16000rpm screamers) have titanium COATED valves. Once the coating wears off they close up valves REALLY QUICKLY!!!!! If the clearances are ok your work was good & at least it will rule out insuficient valve clearance as the cause to your problem.If it still plays up - well then I would use the process of elimination to solve the problem i.e is it electrical,fuel, or mechanical. With valves checked already a compression or leakage test would pritty well rule out the mechanical system.To test electrics on motorcycles without test equiptment & a lotof know how can be difficult & EXTREMELY DANGEROUS( shock hazard 40,000 v+). So I'll try keep it simple. On the web you can purchase ignition spark testers that will connect to any plug lead & cause the ignition system to jump a gap of 6 to 8mm.These are cheap & will test the system as a whole for its performance. Great for a quick check of any ignition system. If the spark seems fine then your left with the fuel system. check for blocked fuel tap,water in tank or carby bowl,blocked fuel filler cap vent,blocked carby vent hoses,accellerator pump function.
I hope this has been somewhat helpfull.
I am happy to help with further questions
Regards Andrew

not sure bout that bike specificaly, probly there is a spring on the gearshift shaft , or something to return the lever and shift drum back whenever actuated. no matter what it is, you gotta split the cases to fix it .