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Mikuni BS32 throttle plate opening at idle

  • Thread starter Thread starter Tony
  • Start date Start date
T

Tony

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Got an '82 GS650GL, Mikuni BS32's, recently un-ganged and dipped. Everything is shiny and reassembled now with fresh brass and o-rings.
My only question is... How far should I screw the idle adjuster in? Or... How open should the throttle plates be on first firing?
My guess is just a "smidge." Basically the diameter of the straitened out pin I used to bench sync them prior to un-ganging.

Even if it doesn't matter, I'd still like to hear what people think.
 
Last edited:
Do you have them on the bike yet? If not, re-do the bench sync, but use LIGHT, rather than anything solid to check the openings.

Hold the carbs up to a light or a bright wall, have the engine side towards you. If you look through the carbs, you will see a sliver of light at the bottom of the plates. By moving the idle speed screw, you can see which carb approaces closed first, then sync the others to that. I find this MUCH more accurate than a pin, paper clip or any other mechanical device.

When you are done with that, back the idle speed adjuster out until it does not touch the carb linkage (cam?), then turn it until it just touches, plus 2 turns. It might be a bit too much, so be ready with the KILL switch when you try to start it.

.
 
Hey! Thank you so much for that! It makes a lot of sense.

The carbs are still sitting on a table so I'm gonna go get to it now!
 
Here is what you will be looking for, the sliver of light under the plate:

IMG_3451.jpg


.
 
Do you have them on the bike yet? If not, re-do the bench sync, but use LIGHT, rather than anything solid to check the openings.

Hold the carbs up to a light or a bright wall, have the engine side towards you. If you look through the carbs, you will see a sliver of light at the bottom of the plates. By moving the idle speed screw, you can see which carb approaces closed first, then sync the others to that. I find this MUCH more accurate than a pin, paper clip or any other mechanical device.

When you are done with that, back the idle speed adjuster out until it does not touch the carb linkage (cam?), then turn it until it just touches, plus 2 turns. It might be a bit too much, so be ready with the KILL switch when you try to start it.

.
Works for me. Pretty much the same way I do the initial bench sync.
 
Got an '82 GS650GL, Mikuni BS32's, recently un-ganged and dipped. Everything is shiny and reassembled now with fresh brass and o-rings.
My only question is... How far should I screw the idle adjuster in? Or... How open should the throttle plates be on first firing?
My guess is just a "smidge." Basically the diameter of the straitened out pin I used to bench sync them prior to un-ganging.

Even if it doesn't matter, I'd still like to hear what people think.

Exactly what do yo mean by "fresh brass"? I hope you didn't install new aftermarket jets.:(
 
Well, you can thank the PO for not including anything original or even close to a correct size. Unless I get my hands on a time machine, these OEM equivalents from Jets 'R Us will just have to do the trick.

But I appreciate your input.
 
Well, you can thank the PO for not including anything original or even close to a correct size. Unless I get my hands on a time machine, these OEM equivalents from Jets 'R Us will just have to do the trick.

But I appreciate your input.

Jets R Us sells OEM for just a couple bucks more then the knock offs. The OEMs are well worth the price difference.
 
Jets R Us sells OEM for just a couple bucks more then the knock offs. The OEMs are well worth the price difference.

Wow, I didn't realize that the two columns were different types. I bought from the left side thinking they were all just "equivalents" and that the list just continued on the right side. I'm surprised, yet grateful, that Mikuni still supplies such things.

I also checked my fittings for the mikuni double-square stamp and they have them. So rest easy guys and thanks for the tips!
 
Wow, I didn't realize that the two columns were different types. I bought from the left side thinking they were all just "equivalents" and that the list just continued on the right side. I'm surprised, yet grateful, that Mikuni still supplies such things.

I also checked my fittings for the mikuni double-square stamp and they have them. So rest easy guys and thanks for the tips!

Good to hear. Sometimes you just get lucky.;)
 
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