Dion Braud

All 8M case hardware is 19 ft-lb All 6M case hardware is 7 ft-lb

It's a cheap China ATV and as far as information and manual that is most likely not happening. I would suggest finding someone local that has experience working on them and have experience in resourcing parts if needed.

Here is a bunch of useful info for you. Including valve lash spec's. 

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That motor uses the more sophisticated ratchet pawl design for the shifter as opposed to a claw/Star design. I strongly suggest you get a shop service manual and go through the transmission chapter pertaining to the shifting mechanism and go from there. Too much to explain here and without you and the machine present its very hard to teach you about handling those little ratchet Pawl's and their springs along with their retention plate.

The 300EX is a manual transmission.

was it the woodruff key on the flywheel?

Ride a well tuned one and you will see why! Its the best engineered 2 stroke quad ever produced. Once the old tech on it is modded to modern suspension capabilities and motor well tuned and or modified its the SH**! Like the one in my avatar! Lol

TRX250R

Good job!

Most likely Carb issue

DO NOT BUY CHINESE PARTS FOR JAPANESE BIKES! I own and operate a Dirtbike/Quad engine machine shop(Cycletech Performance) and have MANY stories about that crap and not many are good! All those Niche cylinder kits are TRASH. Just have the OEM stuff Reconditioned by Myself or someone else. Unfortunately You lost your shirt on this job because some BS Chinese Company made Some money.

Hey there< Just wanted to reach out and say hello from a fellow PA member. I'm the owner/Operator of CycleTech Performance out of Sciota PA so if you or anyone you know need professional work done or just need some advise then give me a shout. Welcome to the group! Dion Braud, (website) cycletechperformance.com