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Well, I finally broke down and bought a set of vacuum gauges from Z1 and attempted to do the sync tonight. The only problem I am running into is that my manual doesn't tell me what the readings should actually be, does anyone know what a 81 KZ1000 CSR with BS34's should be reading?

matched between all 4 carbs. the actual readings will vary depending on engine wear but the main point of synching is to make them match.

Hey I tought there would be a standard but I could be wrong but I believe the readings will be relative to your compression?

low compression = low Vacuum

What jets do you have

Yea, the actual readings are not important. By syncing you are either opening the carb=less vacuum or closing it=more vacuum, trying to get all 4 the same. In theory this would mean all 4 carbs are opened the exact same amount. The problem comes in when you have uneven power in cylinders from wear, then syncing the carbs with the mercury stix can result in really crappy running because one or more carbs may have to be set really different than the others. On my more "wornout" bikes doing a mechanical sync and not doing the vacuum works better.

Kwas wrote:

Hey I tought there would be a standard but I could be wrong but I believe the readings will be relative to your compression?

low compression = low Vacuum

Changing the ignition timing will affect vacuum reading.
Adjusting the fuel mixture will affect vacuum reading.
Changing the air filter will affect vacuum reading.
Changing the exhaust will affect vacuum reading.
Adjusting valve lash will affect vacuum reading.
Barometric pressure will affect vacuum reading.
RPM will affect vacuum reading.
Changing the cams will affect vacuum reading.

Low vacuum will tell you something's not right, but it won't tell you "what's" not right

I am not sure what the jets are on this bike, I haven't taken the carbs apart yet. It was running descently, but vibrating a bit, so in reading i found that it could be the carb sync as my old bike did it until they were synched correctly too (I didn't do it that time). The engine shouldn't be worn, it was professionally rebuild 2k ago, but I have to get a new compression tool today because my other one kind of got killed in the move last month:unsure: In doing the sync, cyl 1,2,3 seemed to be pretty dead on, but 4 was pulling more vacuum though, so I will have to see on how to get this closer then. Would an air leak or something cause it to pull more also?

did you calibrate the mercury first?

use a couple of tees and use one cyl, make sure they are all the same

Your carbs should be bench sync'd FIRST then sync'd on the bike with the gauges.

To bench sync, remove the carbs. Screw the idle screw in a turn or two and then sync 1 to 2 using the adjuster between the two carbs. Then sync 3 to 4 using the adjuster between the two carbs. By sync, I mean MAKE THE SLIDE HEIGHTS THE SAME. Then sync 1/2 to 3/4 using the center adjuster. Make sure you can OPEN the slides some and can close all four slides using the idle screw and they all close at about the same amount. Then open the slides an eyelash... the CV carbs don't take much opening to idle when reinstalled on the bike.

OK, on the bike, the mercury should be about 20-25 on the scale on your manometer at idle. This will go DOWN if you have th idle speed to high so get the carbs warmed and then set idle idle mixture by first turning the idle mixture screws out about 1.5 turns from lightly seated. Go to carb #1 and turn the screw in/out a bit (may be up to 1 full turn either way) for MAX idle speed. Then reset the idle with the idle knob and repeat for carbs 2, 3 and 4. THEN sync and as noted, the reading should be about 20-25 with little difference between carbs.

If you need to adjust, first adjust the sync pot between 1 and 2 and make them the same, then the pot between 3 and 4 and make them the same and then use the pot between 2 and 3 to get all four the same. You will seldom get it perfect the first time and will have to generally repeat this exercise at least one more time (just the sync part and not the idle mixture). Once you have all four the same and in the range noted, rev the engine and make sure that when the idle comes down, all four are the same. If they are not, repeat sync and if you can't get them the same after revving, remove the carbs and recheck the interconnecting parts to see if anything is binding and make sure the return springs are installed properly... sometimes they get knocked off their keepers and will unwind and not be wound properly to get full spring when reinstalled.

Great, thanks for all of the detail WiredGeorge and everyone else, I will check all of this out tonight and get back with an update.

Update - Well, I did all of the steps above last night and took the old girl out for a quick 20 mile ride. It was amazing! Not having any vibrations and the power was smooth all the way through. Thanks everyone for your advice and it brought a whole new life to this bikeB)

WG, is this also known as a mechanical sync? Taking the top of the carbs off and tuning in the throttle slides? I have a book that say's you can do this while they are on the bike with it running. They say to get the vaccuum the same on the mechanical sync and then do the air screws. Does this sound right?

wiredgeorge wrote:

Your carbs should be bench sync'd FIRST then sync'd on the bike with the gauges.

To bench sync, remove the carbs. Screw the idle screw in a turn or two and then sync 1 to 2 using the adjuster between the two carbs. Then sync 3 to 4 using the adjuster between the two carbs. By sync, I mean MAKE THE SLIDE HEIGHTS THE SAME. Then sync 1/2 to 3/4 using the center adjuster. Make sure you can OPEN the slides some and can close all four slides using the idle screw and they all close at about the same amount. Then open the slides an eyelash... the CV carbs don't take much opening to idle when reinstalled on the bike.

OK, on the bike, the mercury should be about 20-25 on the scale on your manometer at idle. This will go DOWN if you have th idle speed to high so get the carbs warmed and then set idle idle mixture by first turning the idle mixture screws out about 1.5 turns from lightly seated. Go to carb #1 and turn the screw in/out a bit (may be up to 1 full turn either way) for MAX idle speed. Then reset the idle with the idle knob and repeat for carbs 2, 3 and 4. THEN sync and as noted, the reading should be about 20-25 with little difference between carbs.

If you need to adjust, first adjust the sync pot between 1 and 2 and make them the same, then the pot between 3 and 4 and make them the same and then use the pot between 2 and 3 to get all four the same. You will seldom get it perfect the first time and will have to generally repeat this exercise at least one more time (just the sync part and not the idle mixture). Once you have all four the same and in the range noted, rev the engine and make sure that when the idle comes down, all four are the same. If they are not, repeat sync and if you can't get them the same after revving, remove the carbs and recheck the interconnecting parts to see if anything is binding and make sure the return springs are installed properly... sometimes they get knocked off their keepers and will unwind and not be wound properly to get full spring when reinstalled.

I may be wrong Vach, but I think WG is referring to the sync on CV carbs and your talking about the sync on VM carbs.

Someone please chime in if I'm incorrect.