I wanted to summarize this in a single post to avoid search time for anyone that may have this issue in the future.

Symptoms: I went from instant start to hard start that was improved by backing out the fuel screw, with no changes in temp or humidity. Obvious and exaggerated decel popping, that is somewhat improved by turning out the fuel screw. Also, exhaust pinging once the engine is off after riding the bike, probably due to running lean and hot. I also started having hesitation from off idle to mid range. Needle changes modified but didn't solve the issues.

Diagnosis: I sprayed carb cleaner on all connections, seals and caps on the outside of the carb with the engine running at idle. No effect anywhere except spraying the piece with the throttle bracket and spring (red arrow below).


Inside is a felt seal behind a plastic "cap"


Solutions: There are several solutions with varying levels of effectiveness. I'll list them in the order I feel they are most effective.

Replace with Yamaha stock rubber shaft seal. Kawasaki doesn't list nor sell this seal separately. Yamaha sells a rubber shaft seal that I used and it fits and works perfectly. Part is very cheap, about $3. You can also get generic ones on ebay.
256-14997-00-00 SEAL $3.01


Replace with Quad section O-ring: Some on the xs650 page have gone with these orings from McMaster-CARR. A lot who did had to replace them again after a few months so I consider this a temporary solution.
McMaster-Carr
McMaster-Carr


Add a #10 regular O-ring to the felt seal: This is what I first did as I didn't have options 1 or 2 on hand. I first tried a #11 o-ring but it didn't seal well enough, #10 oring does. Just add the oring to the shaft seal seat (lube the oring and shaft with silicone spray) and then put the shaft back in with both the plastic cap and felt seal. I did this temporarily until I received the yamaha rubber seal. To be honest, this probably sealed nearly as well but it's best to have a real fix.


Replace with generic felt seals from ebay: I saw generic felt seals on ebay that were the same as the stock one. I chose to go to a rubber seal as thought/felt they are better and folks at xs650 site were having no issues with them. The generic seals might work or might not. I chose not to risk it.


Butterfly Plate Screws: Removing and replacing these screws was the scariest part of the whole problem. These are JIS screws, NOT philips. I stripped them and used a drill bit and extractor. Sounds scary if you haven't done it but it was really really easy to do, to my relief. I replaced the screws with coned hex head screws so I wouldn't have to deal with philips/JIS. I used red loctite and let it dry for a few hours before starting the engine. Been working for 2 months with no issues. When I removed them to replace the oring with yamaha seal the loctite was dry and still holding the screws.




Below is URL of another site with a lengthy discussion regarding the screws and seals, which is where I got most of my information.
(BS series) Throttle Seals: Who's done 'em, who needs to? - XS650 Forum

Here is my orginal thread of this issue: https://www.kawasakiforums.com/forum...ustment-42921/

Hope this helps someone or is at least interesting reading.

cheers

 

Good stuff. Thanks.
Thread linked in the FAQs.

 

Nice! I've been wondering if you had it fixed.
I remember you finally finding the problem.
Thanks for documenting the fix, nice job!

 

I have recently been involved in helping a member setup his '09 carb for best performance. We could not get any "known working" combo to run correctly - the stock needle would run the bike but the DJ wouldn't at any clip setting...

The symptom was stumbling at 4-5.5k RPM under load or at WOT.. In this case, so severe as to make the bike pretty much unrideable. Turns out, after exhaustive troubleshooting, this seal was/is his problem..

There is difficulty with diagnosing this seal when it is leaking. The effect of this air leak goes contrary to conventional "wisdom" . The bike would run fine as long as it was running lean - adding fuel, by way of the DJ needle and you get the "stumbling"..

So point is, if you get midrange stumbling, start troubleshooting by spraying your throttle return spring with something that'll reveal the leak - carb cleaner would certainly work but could possibly damage the seal, He used WD40 - which took a little while to be sucked in..

 

Klxster, I also didn't improve the problem by moving the needle. But I did improve it with the fuel screw. Another symptom I forgot to mention is decel popping, a lot, like a machine gun jaja. I always have some but this was just ridiculous. It was improved a bit by the fuel screw, and greatly by the #10 Oring.

 

Oh yes, decel popping, that is another tell tale. But as we know, that can be caused, or made worse, by the air injection system and/or exhaust leaks.. In the case I'm involved with, the member was still running the injection system. This compounded the problem with diagnosis of a seal leak. Until the system was removed and the fuel screw reset, we could not "drill down" to possible shaft seal leakage..

I also have a theory that this seal leakage could be relatively benign if the bike is making stock or near stock power. But with certain performance mods, the "draw" through the carb is increased - especially at max TRQ RPM's - which causes the leakage to reveal itself as a stumbling as fuel is added to the fueling curve..

Ultimately , the decel pops became increasingly worse even after all measures were taken - which revealed the possibility of a shaft leak..

 

My smog system had been removed long before, glad that wasn't a factor.

Is he ordering a new seal? Has he played with the fuel screw turns?

 

Yes, seals are on order.. Yes, he played with fuel screw.. He reported decel pops were gone at one point, but returned later..
Perhaps PWJM will describe his method of detecting the leak - it is non-destructive to the seal..

 

What's the best way to test for this? Seems like you need a high vacuum situation and I don't think idling makes the cut unless the seal is totally shot.

 

I guess mine was real bad because I tested it just idling. Sprayed carb cleaner on the return spring plate and it would die, while idling only. Also, lean surging when blipping the throttle at idle. Ridiculous amount of backfire at any rpm of throttle.

What are your current symptoms and setup?