I started a project taking an old beat up KTM 50 mini adventure and have been trying to get it running for my kids.  Now I'm way upside down in the thing, solved many problems but one remains.

The bike starts every time.  When cold my kids can ride the bike and it runs perfect at all rpms for approx 5 min.  Once the bike is warm it dies at high rpm (only when warm).  Starts right back up and idles fine runs fine up until about 1/4" throttle but dies once the throttle is opened any more.  I just threw another $125 at a new coil, swapped it out today and the problem remains.

What I've done:
-New Cylinder
-New Piston
-New Coil
-Cleaned the carb 3X
-Drained the Gas / New Gas
-New Plug
-Did a vacuume leak test w/starter fluid
-Verified choke is working properly

I'm out of ideas.  Need some collective brain power... thanks!

It is probably the stator.  Very typical ktm 50 problem.

kdub442, on 28 June 2012 - 09:11 PM, said:

Thanks kdub442.  Looking at the fishe I cannot determine which part is the stator.  None of the parts descriptions at the bottom are labled as a stator.  See link below:
http://www.motosport...S5_E?fam=Engine

Edited by BikeNutz, 29 June 2012 - 06:04 AM.

Wow, tough to tell from that diagram, but it's #54 - ground plate ignition coil.  You could use an Ohm meter on it first, to see if it's bad.  But, you'd have to search for what it should be (I'm not sure on that model - I've got a 2008 50 Sr).

Wire brush the thing like crazy before you buy another one.  Every two or three washes i used to pull the stator off, wire brush it, and then squirt wd-40 on it and wipe it off.  Seemed to help them last longer.

I cant remember how to ohm it exactly. bu you needed to pull it out of the bike and measure the resistance between the lug and the areay you put a bolt on.  I used to pull the whole thing out to take the coil out of curcuit.

After trouble shooting this more I think I may know what the issue is.   I think the ring gap is incorrect (too tight).  I think the motor is actually seizing then cooling down quickly and able to start back up again.  If I try to start the bike immediately after (within 10 sec.) I can feel additionaly drag.  By approx. 30 sec. later the motor cools down and is able to start and idle fine.  I'll post back once I have had the chance to pull it apart to verify.

my sons 03 senior adventure was doing something similar, but it was a gradual loss of power, then finally would barely move. started and idled fine - just no power - cleaned carb - changed plug - checked ignition.  Thought it was a worn top end - started taking engine down, pulled the pipe -and
holy cow that expansion pipe was just about plugged solid with carbon.  (i'm a mechanic by trade and have never seen anything this bad).  cleaned it out - runs like a scalded ape now.
p.s. - had beed running maxima 927 (castor) at 32:1
   - also my son always ran the crap out of it
have since switched to maxima super M