may be time to pull the clutch cover and inspect the shift shaft, flange, the springs that return it to it's nuetral position, the shift star and it's wheel/detent thingy that keeps it in gear
seeing the shifting action is much easier with the clutch pack removed, and you'll need to be turning the output shaft (engine sprocket) for it to go thru the gears with the engine not running, this can be done with chain removed and turning the sprocket, or up on jack and turning the wheels.
the shift flange thingy is returned to it's nuetral position by 2 small springs on the flange near the shift star, if it doesn't return to this nuetral position, it will not shift to the next gear, this can be tested by physically returning the shifter to it's nuetral position with your foot, (down if shifting up, or up for down shifting) then it should shift to the next gear.
if thats the case, you can check the 2 small straight springs are hooked around the inside of the flange.
in my case a used replacement shift shaft was the fix, check on here or ebay.
(all references above to "nuetral position" refers to the position the shift shaft/detent sit normally, not nuetral of the trans gears)
the KOR engine assembly vids show how this all installs........
http://www.blasterforum.com/threads/kor-engine-assembly-vids-no-crank-puller-needed.51169/
