Syncing KZ750 (four) carbs?

I'm a pretty good car mechanic, but am somewhat new to motorcycles. The '82 KZ750 I just got (4 cyl) runs a bit hot, shakes a bit especially in the lower rpm's, and rattles the primary chain a bit, also at lower rpm's. I was told by a friend that syncing the carbs might clear a lot of that up. My idea of syncing carbs is that they all open the very same amount and provide the very same amount of fuel, at the same time. From my reading, it appears that special tools are needed that I can't afford, let alone paying a shop to do it.

I want to try this, but is there any simple (or simpler) approach to doing it?

If the engine is in fairly good order, ie (compression, ignition, carbs REALLY clean). Then a good bench sync will provide a rideable starting point. Depending on the type of carbs - do you know which ones you have?

If your not sure about the engine, then you will need at least 2 vacuum guages of some kind, and hoses that have restrictors. Restrictors can be made easily of you choose this route...

Some people purchase or make homemade devices called manometers, but a set of vacuum guages will work fine, and are less likely to cause damage from fluid passing into the engine.

The '82 KZ750 I just got (4 cyl) runs a bit hot

- I doubt a sync will affect this very much, but these bikes do tend to run pretty hot normally. At normal temp you should'nt be able to touch the block or head, and feel the heat rushing past your ankles while riding.

shakes a bit especially in the lower rpm's, and rattles the primary chain a bit, also at lower rpm's

- This can deffinately be attributed to carb sync, however I would look into the cam chain tensioner 1st, and make sure it is operating properly before making any other adjustments. Very important!

Good Luck!

With an 82 750/4 you probably have the Keihin CV34 carns like me. Possibly have Mikuni BS34 if a PO swapped them in.


IMHO that the only way to synch properly is to use a the 4 vacuum gauges. I have the morgan carbtune. If something like this is out of your reach then maybe do a search here as there have been many posts from people who made their own devices using tubing and heavy oil.

Also, perhaps there a member living near to you who has a set of gauges ?

Not yet sure which carbs I have, I'll check today. How is a bench sync done (can't find that in my book)?

polkat wrote:

Not yet sure which carbs I have, I'll check today. How is a bench sync done (can't find that in my book)?

If not already familiar, the search function may be very helpful in linking to existing threads on any particular subject.

In this instance, would suggest typing bench sync in the search box, then clicking Go. And find some excellent and very informative articles.

Imo, the KHI official Kawasaki Motorcycle Service Manual for a particular model is superior to the aftermarket manuals. And regularly appear on ebay.

Good Luck!

[Click on image to enlarge view]

The Keihn CV34 carbs on my 83' 750-4 are a lot easier to vacuum synch than the MIkunis on my 650. You can do a great job with the clear hose and oil setup, syncing two carbs at a time; 1-2, 3-4, then 2-3. As was mentioned prior, search here and there are plenty of old posts on it.

Okay, I did the 'bench sync' search and read a lot of posts. My carb background is in car carbs (which I'm pretty good at), but my motorcycle multi-carb experience is pretty much zilch!

It appears the idea of bench syncing is to get all the sliders at the same height at idle....right? Few if any of the posts were clear on this. Some talked about using drill bits and letting the sliders drop on them then adjusting.... something, until all the sliders had the same pressure on the bits. Well, seems to me it would be little more then a guessing game testing that pressure with fingertips! And I didn't fully understand just what was adjusted to do this.

There was also a lot of talk about manometers, but little or none on where to hook them up, what to look for, and what to adjust while using them.

Is there a website that any of you could guide me to that explains this better?

www.vfrdiscussion.com/forum/lofiversion/index.php/t16200.html

That link shows a 4 carb manometer setup used to synch a Honda. It's the same principle you'll use for the KZ.

Your vacuum ports will be on the engine side of the carbs. Some ports may be hooked to an emission system, Carb #2 goes the petcock, or plugged off. Look in your manual or go to www.wgcarbs.com for pictures. www.wgcarbs.com/index.php?option=com_con...view&id=25&Itemid=25

There are three screws with locknuts you will adjust. One screw will synch carbs 1 & 2 together, the other synchs carbs 3 & 4 together. The third will synch the two sets together, 1-2 to 3-4. These screws are located on the engine side of the carbs.

So build a manometer, synch 1-2, then synch 3-4 then adjust the middle screw to get the two pairs synched. Using oil in the manomete, you can get the levels within a centimeter of each other, are good.

What year KZ750 four?
Original carbs?
CV or manual slide?

With above info, may be able to provide an exploded view diagram for part reference, sync advice, etc.

Imo, will always be fighting a losing battle without the FSM, regardless of whether dealing with carbs or other components.

Good Luck!

So you need to sync your carbs for whatever reason. If you make a light oil manometer it has to be at least a yard tall. And I don't care what the pressure is I want to see the difference between the carbs. So for under $12.00


Baby bottles: I bought a pack of three for $3.36 They're even marked in ozs and mls.
#7 rubber stoppers: you need two ($1.99 ea at lowes)
3/16" or 5mm id clear tubing: I used 2 yards
liquid: I used mineral oil colored with food dye



Next I drilled two 5/16 in holes in each stopper. (These holes need to be the same size as the od of the tubing your using.)
Cut off about 20 in of tubing and use it to connect the two stoppers. You want enough tubing inside the bottle so it almost touches the bottem of the bottle. Cut the rest of the tubing in half and connect each to the stoppers so the tubing just clears the stopper.



Add about 3 oz of your fluid (I used mineral oil colored with food coloring) to each bottle.

Connect the bottles to the intake (If you have more than two carbs your manual tell you which carbs to start with) and start the engine. Any difference in pressure will transfer fluid from one bottle to the other. And as long as there isn't enough fluid to fill either bottle, you can't suck any fluid into your engine. The water based food coloring will separate from the mineral oil. So after a couple of hours there is a blob of food coloring. Just shake the bottle and the blob breaks up into thousands of tiny drops of color, just perfect for seeing which way the fluid is traveling between the bottles.

Okay! These are the kinds of responses I can work with! I'm still not sure what kind of carbs they are. The bike is an '82. The picture of the CV34's in the website OKC-Kent provided are a visual match for mine (but are there any marks on the carburetors identifying them)?

Johnj's manometer pics are quite nice and I'll no doubt copy that.

Thanks for all the help guys!

If your carbs are Keihins it should say so on the #1 carb. The #1 carb is at your left knee as you are sitting on the bike. Look just below the shiny chrome carb top and just above the choke lever. Just forward of the word Keihin should be a brass nipple which will have a rubber vacuum cap on it. This is where a manometer would hook up. Each carb will have similar nipple. The nipple on the #2 carb may be connect via a vacuum line to your petcock.

Most of the posts here which talk about bench synching are referring to Mikuni carbs where the throttle cable pulls a slider up or down. I could be totally wrong here not having experience with Mikunis. The Keihins are a bit different in that the throttle cable works the throttle flaps or butterflies and a vacuum operates the sliders. Anyway, I've never been able to figure out how I might bench synch my Keihins with any accuracy. About the only thing I can with carbs on the bench is set the fuel level.
Good luck