XS650SK Carburetor Jetting Confusion

jetmechmarty

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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.
View attachment 183947
No washer either!
 

gggGary

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Jim

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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.......
View attachment 183948
I've called it a mix screw for about 50 yrs now. Ain't about to change now... :rolleyes: :boxing:
 

5twins

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"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.
 

5twins

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For the mix screws, I've always used a generic 1mm x 3mm o-ring, but that little washer will be tough to source .....

FkIevlH.jpg


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

AbOWaij.jpg


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
 

650Skull

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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

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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.
 

Jim

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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.
 
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