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Rear Shock rebuild and some other issues

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I was trying to get a new 5.9lb spring on the stock shock that came on my 2009 KX250F that I recently traded. 
The bike appeared to be in OK shape but while digging more and more into it, it seems to have been a little neglected.

Had starting issues which prompted me to swap out the PJ for a #42, and clean the carb (found the diaphragm was a little worn on the ... have a replacement that I'll be putting in shortly). 
Engine does run ok but sometimes hard to start (either hot or cold, doesn't matter, it'll start one kick then won't start at all 10min later...). 
One of the intake valve is out of specs (at +0.18mm over spec) so that's going to be correct next.
Just not sure if the conditions above would cause the issues starting.

Front left fork is leaking a little so i'll be replacing the seals... Not sure if I should plan on getting anything else besides oil, seals and dust covers for it.

Rear shock: was going to take the rear spring out (stock) to swap it for a 5.9lb from factory connection (current spring had almost no free sag and appeared to have preload and compression bumped up to compensate for higher rider)... wanting to make things right I got the proper spring.
While taking the spring apart, bottom lock nut was completely seized up... had to cut it in half. Finally got the spring out, then quick test revealed that the shock would no longer expand on its own! 
Took the shock apart, oil looked very clean (likely serviced not too long ago), no leakage at the rod, rod appears to be good conditions however upon removal I noticed a large scratch inside the shock cylinder.

At this point I've already ordered a use replacement, but trying to debate if i need to put any kind of money into this one and rebuild it to use as a spare. Was thinking about maybe honing the shock cylinder, just not sure if that can be done to stay within specs. 
Other internals look pretty good.

Any pointers would be appreciated.

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Hi samW,
Good discussion points. Summary;
- the carb is cleaned and new pilot jet
- the rear spring is too stiff
- the rear shock is worn yet seems good. They do not always self expand btw.
- motor runs but starting is inconsistent
- clearance on one intake valve is over (big gap)

Not sure what the actual questions are ... yet here goes.

Shock/spring. Drain it, flush it, refill, put your weight spring on. Use it. Unless you are a top tier competitive racer, really nothing to concern with. Shock is a shock, set the clickers to your ride preference while out for a rip.

The valve, triple check, triple measure, re-shim as required

The starting problems, dump entire old tank of fuel and put fresh in. Check that hotstart is sealed and not leaking, set the fuel screw at 2.75 turns out, needle at second clip from the top, idle speed once started set at a healthy 2200 rpm range; tune fuel screw to your liking from that beginning point.

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I guess the questions were as follows:

-shock: should i be concerned about the big scratch inside the shock cylinder? (I've since replaced it with a 2013 model that is extending on its own so definitely in better shape it seems).

-valve clearance, is planned for this winter most likely but I'm trying to figure out if I can postpone it till then (motor doesn't pop or anything else when it runs).

-not sure if anyone else has any suggestions regarding the inconsistent starting issues (I just finished cleaning up the carb and replacing the diaphragm, hopefully this will help).

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The shock has a bladder in it that is pressurized.  All that does is help to keep shock oil from foaming as it gets hot if riding really hard, lots of bumps.  Basically, it is added pressure to keep the oil from boiling.  Through the valving the whole shock is pressurized by this, not just one side.   A scratch in the cylinder has little effect on this purpose of the pressure.   What a bad scratch will do is marr the piston parts, reducing the seal, adding bypass route for the oil.  This will act like softer valving.  Depending on the size of the scratch, it can be smoothed out so as to not cause damage and wrt the ride firmness the clicker adjustments can be more than enough to compensate for some leakage.  So the answer I guess is; depends how bad the scratch is and whether it is causing piston damage or not.

All components and aspects of the starting issue is covered (condensed) above, let us know if you need more detail.


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anything special to smooth out the scratch? Piston looks fine, even the seal on it. 
I was going to get a drill attachment honing tool to get that repaired and rebuild the shock and use it as a spare if needed.

As far as the carb, all of these have already been checked but I suppose with carbs it's easy to overlook something. Hopefully the last cleanup will do the trick, if not i'll try again and replace more orings.

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The shock shaft should come back out on its own. When the shock compresses it reduces the volume available inside the shock (displaced by shaft volume)  and pushes fluid into the reservoir compressing the shock bladder. My guess is who ever serviced it under filled the shock oil.

Edited by lumpy790

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