Blaster wont shift

[Brandon308]

So i bought y first blaster in the summer. It was pretty beat up but since i got it i been cleaning it up a lot! I let my buddy use it the past few days and for letting him ride it he said he would change the transmission fluid for me. He accidentally put 2 STROKE OIL in the transmission and he only road it for maybe 5 mins because it wouldn't shift out of 3rd but it would shift threw 1N23 but not out of 3rd. so i flushed it with a new bottle of 10w30 and filled it up with a new bottle of 10w30. Now it wont shift and have no idea how to fix it. im pretty mechanically inclined so i sure i can fix it i just dont know how. any help would be great.

 

[Larry's Shee]

Welcome !!

Either drain the oil or lay it over on the left side so you can take the clutch cover off.
Turn gas off. Clean excess dirt off, remove clutch cover. Inspect that shift star screw is tight, inspect rest of external shift mechanism is not broken or excessively worn. If screw is loose, clean screw and drum hole with brake clean or simular, let dry , use loctite on screw. Check in manual for how everything should look.
Also make sure clutch is adjusted properly.
Presuming you checked that shifter is tight on shaft.
Is this with shifting normal or speed/power shifting?