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Bench Syncing 19 Nov 2010 16:28 #413469

  • BIGKEVIN
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I have 29 mm Mikuni carbs on my 1976 KZ900. I just cleaned the carbs and trying to do a bench tech on them. I head that you can use a 1/8 inch drill bit to set the height. When setting the height, do you set it from the pod side or the intake side ?
1976 KZ900
2006 ZX6R

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Bench Syncing 19 Nov 2010 17:14 #413473

  • bountyhunter
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It's been a while, but I think I did it from the air filter side.
1979 KZ-750 Twin

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Bench Syncing 19 Nov 2010 17:17 #413475

  • BIGKEVIN
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I was reading other posts and it side to set the height on the intake side. That would be on the opposite side from what you are saying. I dont know, just trying to find out.
1976 KZ900
2006 ZX6R

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Bench Syncing 19 Nov 2010 17:32 #413477

  • larrycavan
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If you use a 1/8" bit, you would have to do it on the filter side of the carburetors.

That's way too large for the port side.

If you do the port side, use a tiny bit. :)

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Bench Syncing 19 Nov 2010 17:34 #413478

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OK, thanks.
1976 KZ900
2006 ZX6R

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Bench Syncing 19 Nov 2010 19:21 #413489

  • stonemaster
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welding wire is a good choice as well, i used .025 but on urs .030 might be the choice

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Bench Syncing 20 Nov 2010 04:09 #413513

  • Jeff.Saunders
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I just use a small paperclip - partially unwound - then it has a handle on it...
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Bench Syncing 20 Nov 2010 04:40 #413516

  • JMKZHI
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When done correctly, bench synching the carburetors w drill bits does not set the gap to the width of the drill bits... Any size drill bits can be used, even 1/2" if that's what you have. The purpose is to set them all the same... quickly. Personally, I found doing all four w a wire gauge tedious.

I believe you place the drill bits on the engine side carb bore - they may not lay flat on the airbox side.

Bench synching carburetors using 2-4 drill bits.
Here's how I do it: (credit to MurphyAU from whom I got the idea):
(1) Remove the throttle pulley spring temporarily to make the job easier & so that the slides don't get buggered, particularly the notches if your carbs have them.

(2) Loosen the locknuts & eyeball all four slides real quick-like so that the gap is about the same, then quickly set one using the wire gauge - it doesn't have to be perfect - tighten the locknut - you're done adjusting that one which is now the reference carb.

(3) Raise the slides in unison w the throttle pulley and place & keep one drill bit in the reference carb, then lower the slides in unison until the reference slide touches the drill bit.

(4) Next, use a second identical drill bit to adjust the second carb so that the slide touches the bit - it should be the same as the reference carb w both slides resting on the drill bits. Tighten the second locknut - you're done w the second carb.

(5) Do the other two carbs the same way - one drill bit stays in the reference carb, while the second drill bit is used to set the others.

(6) Remove the drill bits, then lower the slides. All four should be the same & the gap should be whatever size gauge wire you used to set the reference carb. Reinstall the throttle pulley spring.

(7) Please note that this method does not set the gap to the width of the bits - you can use any size drill bits. Also, you could use 4 identical drill bits. And beforehand, make sure there's plenty of adjustment available in the idle adjusting screw in either direction.[/quote]

PS: it's much easier & faster to do than it is to explain it.

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Bench Syncing 20 Nov 2010 04:58 #413517

  • Patton
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From Sudco Mikuni Tuning Manual 4th Edition as to bench syncing Smoothbores.

Note this is done from engine side of carbs.

I use same method on Mikuni 26mm oem manual slide carbs on KZ900-B1 LTD.
And would anticipate using same method on virtually any manual round slide carb.

Also avoids concern or contending with cutaway on intake side of throttle valve (slide).

Good Fortune! :)

[Click on image to enlarge view.]

1973 Z1
KZ900 LTD
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Bench Syncing 20 Nov 2010 05:08 #413518

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JMKZHI wrote:

...And beforehand, make sure there's plenty of adjustment available in the idle adjusting screw in either direction.

Important for later running vacuum sync, when height of throttle slides will typically be adjusted both up and down with the idle adjusting screw.

If the slides are too high, but further lowering is unavailable due to being out of thread on the idle adjusting screw, =SOL :pinch:, and repeat bench sync.

Good Fortune! :)
1973 Z1
KZ900 LTD

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Bench Syncing 20 Nov 2010 05:26 #413520

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After bench sync (equal slide heights), the engine running vacuum sync will usually result in the slide heights being no longer exactly equal, as each individual slide is minutely adjusted to best equalize performance among the cylinders.

The bench sync is a base line setting, to work from in later performing the running vacuum sync.

Many folks are able to just eye-ball the gaps and get them equal enough (without using wire or drill bits) to later proceed with a successful running vacuum sync.

Good Fortune! :)
1973 Z1
KZ900 LTD

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Last edit: by Patton.

Bench Syncing 20 Nov 2010 11:09 #413570

  • JMKZHI
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The drill bit method is handy for the first timer who would probably be a bit leery of eyeballing the gap. After doing it for my VM24 carbs, the bike fired right up & idled fine. When I connected a homemade synchronizer, the fluid level in the tubing didn't move very much or very fast.

Some folks say the mechanical synchronization is a waste of time, but I found it helpful because it kinda gave me some practice in setting the slides. Also, a beginner w a mercury manometer would be well served to go ahead & do it, instead of taking the risk of sucking mercury into their engine.

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