crossposting here from DS650.org the following is a copy paste from

Transmisison issiues

TLDR; my bike pops out of gear all the time, thinking worn 3rd or shift forks

want to keep downtime under a month should i buy a new transmission or just shift forks or 3rd gear

is there anything else i should do in the engine since the case will be cracked open


THE PROBLEM: >

I bought this bike ('01) used for a great deal. Ive put about ~40 hours on it and this problem has only gotten worse

It is VERY hard to make it stay in 3rd gear, sometimes after shifting or shortly after it will pop into false neutral and bounce off the rev limiter (tell i let off the throttle)

some times it pops up in to 3.5th (shifting up puts it in 4th) but most of the time it goes down into 2.5nd (upshifts back to 3rd)

it has never popped out of 4th
it has never popped out of 5th
it has never popped out of 1st
it may have popped out of 2nd once but i dont think so

I need to fix this because i end up dragging up a steep dune and popping out grabbing the clutch and slamming it back in gear with a little grinding to try and make it.

if i shift up from second and hold it i notice sometimes a few seconds after i floor it their is a second clunk like its shifted again but it has not

what i do now is shift up to 4th from second and down to 3rd as fast as i can and hold the shifter down after shifting, it has never popped out when doing this

also i can only shift into neutral with the engine off or rolling fast, clutch pack is worn so i think thats the problem i use mobile 1 R4T full synthetic wet clutch motorcycle oil 10w-40 so i dont think its friction modifyers, i also have a used great condition clutch basket i will put in with the new clutch pack some day


WHAT TO DO ABOUT IT: :-\

I assume that either 3rd gear is worn and/or shift forks are bent

Options i am considdering

1: Buy a used transmission from a 05-07 bike

2: replace shift forks with the upgraded ones

3: replace 3rd gear

5: do number 2 plus number 3


I want to keep costs under $200, if i do everything (used transmission + new clutch pack + oil) my limit for parts is $500

 

Fix it, Replace the shift forks and get the gears back cut by Mr. HP (Eric Oldham). If you buy a used bottom end (Transmission) you could have the same problem in a short time again. Once the gears are back cut and forks replaced it will shift like butter and it snaps into every gear.
If you have it all apart no better time to freashen up the engine as well - new rings - Piston?

 

I got a beautifull 05 transmission so it has the stronger shift forks

How will cutting the gears help?

Will be putting in new rings

How much will a simple JE 11.5:1 affect the motor?

I can run a mix of clear and avgas to get 91-100 octane when I'm at the coast but would like to be able to go trail riding in the winter on 91 octane clear without fear of detonation

 

The ebay JE 11.5:1 piston kit is actually close to 13:1. Also the head gasket in this kit is incorrect and will cause the piston to hit the head.

You will experience detnation on pump gas and possibly damage to the head and piston with this kit.

MrHorsepower

 

what about the kit from JE themselves or speedsupplies.com

i was not aware the ebay kit came with a gasket and was planning on going OEM gaskets for the bottom end and cometic or OEM for the top end

i expect my piston will need to be replaced since it appears it has a lot of hours on in, the front tires were VERY worn and ive put closer to 50 hours on it since i got it

all i need help with now is what piston and gaskets to get

 

Once again the JE piston is aprox 13:1 and can not be run with pump gas. Its a direct copy of the old HPR 14:1 with .040 machined off the dome. I can get you the correct setup for pump gas. My email is omwracing@yahoo.com. DONT run a stock replacement cometic head gasket its only .027 thick.....WAY too thin.

MrHorsepower

 

Follow what MRHORSEPOWER has to say and you will be setup with the correct parts for everything DS650wise.

 

MR. HP (Eric) is the man. You can't go wrong with his parts and service. Back cutting the gears makes it go into gear easier and you will never miss a shift again. Worth the money if you have it apart.
My 2000 DS with a 730 kit in it from MR. HP has been together for about 7 years - still runs like a clock and starts on the first turn.
Give him a call.