'77 kz1000 Carb sync. Cylinder #2 unsyncable.

More considerations to the original post; possible spark issue causing that cylinder not to fire properly. Also try moving th vacuum line to another gauge. Its possible to have a faulty gauge.

I would never take carbs off a running motor to bench synch... That is the only purpose of a bench synch, to get the carbs close enough to allow the motor to start and run....
And no matter how you spin it when you vacuum synch, you are mechanically moving the physical location of the slide to achieve the desired amount of vacuum, the mechanical measurement of slide location goes out the window...

So just how does adjusting the idle mixture screw change the mech. sync ??????
Depending on the type of carb the mixtre screw is just an air or fuel bleed
There's no way in hell adjusting it will change the mech. sync.

Damn people if you don't know what your talking about don't post just to hear yourself talk

Calm down guys! No need to get angry.

Rage wrote: I recently rebuilt the and cleaned the carbs on my '77 kz1000 A1...Runs fine. Went to sync carbs. Readings
Cylinder#1- 23 cmHg
Cylinder#2-21 cmHg
Cylinder#3-10 cmHg
Cylinder#4-21 cmHg

Factory manual says to set vacuum between 20-28 cmHg. But there isn't enough screw to adjust the one carb. You guys think its a vacuum leak or valve lash on the one cylinder or what??

Could be either or both.

Maybe weak spark for whatever reason on #3 plug and/or low compression for whatever reason on #3 cylinder.

Fuel levels within specs?

Pilot adjustment screws at 1¼ turns out from lightly seated?

#3 carb pilot circuit not yet perfectly clean?

Good Fortune!

Yep. No anger here. I'll be interested to hear what Rage, the OP has found.

Fuel Mixture adjusted for max vacuum is different than the fine sync with gauges adjusting the slides. I think we were just talking about different things.

Happy diagnostics!

Per the FSM when doing a vacuum synch there is no mention of mixture screws, it clearly states to loosen the locknut and adjust the slide position while watching the vacuum gauge.... That is how the slide location changes.... Not really that hard to understand :ohmy:

Obviously some confusion going on here. Yes, when doing vacuum sync on VM26SS carbs the slide height is adjusted up or down to change vacuum readings. The mix screws should be set before and then again after but not during the vacuum sync, according to the manual.

Now....I would still suggest a bench sync to be sure its not a simple mechanical problem. It's not like its hard to do and with PODS it only takes about 2 minutes to pull the carbs. If he is trying to vacuum sync and is out of adjustment it could be something mechanical going on in the carbs. When I got my bike the PO had bent the little tab inside that moves the slide on the #1 carb. This caused me to not be able to even bench sync my carbs, took a little looking to find the problem. If I had been trying to vacuum sync and ran out of adjustment and then started chasing air leaks and who knows whatever else, I would have been chasing my tail around. Who knows what a PO has done. If it's not something like that then fine, at least its ruled out.

Plus a good bench sync makes sure you have the slide height set to a place where you will still have plenty of adjustment either way on the idle speed adjusting knob.

Putting all that aside, he probably isn't even ready for a vacuum sync anyways. Has anyone bothered to read the manual? I didn't pull that list of Preliminary Checks out of my butt. Seems people always want to vacuum sync their carbs first thing....why? Because you get to use fancy gauges and feel like a real mechanic? You're wasting your time. There are 9 separate items listed in the FSM for preliminary checks, many of those are multi step processes themselves. Then after you do those you get to the initial synchronization-mechanical, idling adjustment and then finally fine synchronization-vacuum. That's straight out of the FSM for a 1977 KZ1000A, I'm reading it right now on pg.18. It does state that mechanical sync may not be necessary, but I would still do it if it were my bike. There is no telling what a PO did to the carbs, I would want to be sure they were mechanically ok before going any further.

When I bought my bike one of the first thing the PO told me was that he had been trying and couldn't get the carbs to sync up. He had so much wrong with the carbs there was no way they would even sync up. (including broken tip of one mix screw stuck in carb, the other three bent because he had them closed so tight, main jet for one carb was loose sitting in bowl, dirty dirty dirty, even though he said he had just cleaned them, and on and on etc etc )

That's why I think it's funny to see people talking about syncing the carbs up on the bike they just got and they haven't even checked the air pressure in the tires or changed the oil yet.....but better get those carbs synced right away! (not saying that's the case with the OP, just saying I've seen it on this forum a few times)

All of this is pretty much useless to be arguing about anyways as the OP doesn't even seem to be interested in this thread himself. He started this thread a week ago and never bothered to post another comment in it.

undiablo wrote: Calm down guys! No need to get angry.

Not angry just a fact if you think turning the mixture screw
will change the mech. sync you're a dumb ass.

Sorry I haven't posted any updates to this thread. Been away working. Going to answer all the questions and comments I can in the order that they were posted in the thread.

74ullc- Yes I did bench sync the carbs using the wire method in the FSM. My mistake with the title of the thread it is indeed carb for cylinder #3. Now according to my manual, which is a '78 kz1000 A2a manual, the carbs came stock with a 102.5 main, 15 pilot and 5CN7-4 needle. There must be a slight variation between the US models and the Canadian model. Both my '77 and my '78kz1000's came with 105mains, 15 pilots and 5DL-31 needles.
I did take the carbs off the bike and check the linkage. And indeed carb #3 had a bit of a bend in the link between the plate that screws to the throttle valve and the upper linkage. I straightened re bench sync'd and still not sync able. It did help a little though.

650ed- These are the original carbs for sure. Bike was a one owner and only has 18000km on it. The carbs only have the 3 vents to atmosphere. I didn't check the carb boots for leaks as I actually had a brand new set still in the wrapper I was going to use on another bike. I just put the new ones on. Didn't help.

GregZ - The bike had pods on it when i bought it. All I've done is replaced the dirty, clogged, old ones with new ones.

74ullc - Once again my mistake. It seemed to be idling fine. The bike was definitely running very lean on the main circuit. I have since up'd the pilot to 20 and the mains to 135. I believe the pilot circuit is running too rich because it won't start with the choke on and when it's idling and you put the choke on it just dies.

Anywho to sum up.
- Float bowl fuel levels are within spec
- pilot jets up'd to 20
- mains up'd to 135
- new carb holders
- was bench sync'd before I tried to vacuum sync
- ignition is good.
- Pulled the plugs this last go around. 1,2 and 4 looks to be running a little rich and 3 looks lean. But the plugs are all in good shape.
- Engine oil level is good
- Pilot adjustment screws are 1.5 turns out from lightly seated

Only things I haven't checked yet are compression and valve clearance. I apologize for the long post and appreciate the input. Thanks guys.

Rage

You say the carbs have 3 vents to the atmosphere - something is wrong, there should not be 3 vents. Please show a picture of what you believe to be vents. Ed

650ed here is a pic of the carbs. I circled what i believe to be the vents to atmosphere.

Rage