XS650SK Carburetor Jetting Confusion

Are you sure? The (now disk shaped) o-ring (and often the shielding metal washer) can only be fished up out of the well by a tiny hook. Bend one up out of safety wire.
Second from left in this line up of special carb tools, cleaners.
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No washer either!
 
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There is no such thing as a mix screw.......Pilot screw allows more of the mixed air/fuel mixture into the throat of the car........if anything it would be a flow screw.......
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I've called it a mix screw for about 50 yrs now. Ain't about to change now... :rolleyes: :boxing:
 
"Mix" screw is just slang for "mixture" screw, much better than calling it an "air" screw like many do. That's really wrong. I call them mix screws too.

Marty, with no o-rings installed and those incorrect pilot jets, I'm surprised the bike ran as well as you say it did. I might have expected it to maybe run OK at higher RPMs but have idle issues.
 
For the mix screws, I've always used a generic 1mm x 3mm o-ring, but that little washer will be tough to source .....

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You're probably a good candidate for complete replacement assemblies, quite a bargain actually .....

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https://www.partshark.com/oemparts/p/yamaha/12r-14105-00-00/-pilot-screw-set

I'm really surprised Yamaha never listed this part on the 650 carb diagrams. They show it on about a bazillion others, lol .....

https://www.partshark.com/oemparts/partsearch/yamaha?partsearch=12r-14105-00-00
 
I stand corrected, once again! :notworthy: There are no packings under the pilot screws.

Just a pet peeve Marty..... .

Jim
Just because you call something a name for 50 years doesn't make it something that it isn't...........i know what you talking about when you mention the mixture screw.

For a debate why isn't the pilot jet called the mixture jet.......It allows air in and directly mixes it with fuel before delivering it to the inlet

Gary,
Using your reasoning, the a carb should be called a fuel air mixture box, because that is all it is doing mixing fuel and air.........
 
Jim
Just because you call something a name for 50 years doesn't make it something that it isn't...........i know what you talking about when you mention the mixture screw.
Some (most?) of the carbs I've worked on only had 2 jets.... the idle jet and the main jet.... pilot sits in the cockpit :whistle:
To adjust the idle mixture, you turn the idle mixture screw.... or "mix" screw if you will. Most of the Holley's, Rochester's, Marvel Schebler's et al.... didn't have a "pilot" jet, they had idle jets.... and therefor an idle "mix" screw. Just because Mikuni want's to reinvent the wheel, don't make 'em an "industry standard." I'll go with the rest of the world an call it a "mix screw" .... just like I taught from a textbook.
 
Fwiw... I understand that Mikuni's "pilot screw" is just regulating how much of the "already mixed" mixture flows .... but that flow goes into the venturi to adjust the "mixture" that goes into the cylinder. That makes it a "mix" screw.
 
@5twins to the rescue again.
No, the air jet is not the same style as the main jet used in your BS34 carbs. Your mains are the large round main, the N100/604 type. The O.D. is too big to fit in the air jet hole .....

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You can probably remove the old, worn out foam from your filter "cages" and re-wrap them with new foam. UNI sells bulk sheets of filter foam. It would probably cost about half of what new filters would.
A recap because I don't know what thread this was in. My bike was running perfectly. 56 mpg. No color on the plugs. The stock headers are trying to turn blue. I went one size up on the slow jets and one size up on the main jets. This caused a slight stumble on the crossover and fuel economy dropped well into the forties. @5twins responded in whatever thread I posted in. At his recommendation I went back to the previous jetting and changed the air jets to 130 from 135. The bike still runs near perfectly and I have color on the plugs. I may try 132.5, but for now I'll leave well enough alone. Thanks to all of you who make it your business to help keep these things going.
 
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