Synchrozing trouble

Hi all,

I've got an '82 KZ750 E3 with CV34 carbs. I'm trying to get my carbs synced up to smooth out the idle just a little bit more. I made a manometer with some clear plastic tube, a few T-connecters, and ATF as the fluid. So I should be able to compare vacuum on all four carbs at once.

My issue is this: Everytime I try using it, the vacuum is too great, and the ATF is sucked up any number of the hoses within a second of starting. The only solution I've found is to install another T connecter in each tube, left open to the atmosphere to reduce the vacuum on the ATF. This, however, is giving me issues of its own, and I can't seem to get it to quit backfiring and changing idle speed.

I've been idling it anywhere from 1500-2000 RPM for the adjustments.

Any suggestions? Should I just bench sync with some bailing wire?

I recall making a manometer once using clear tube shaped like a "U" with one side open to the atmosphere and the other being the vacuum measure tube. You hold it with the water level (in the bottom of the U) then put the end of the tube in the vacuum and measure the difference in height of the two liquid levels. You can make the vertical tube sections taller if the vacuum is pulling the liquid too high.

I don't think you T connect anything, I think you make a separate one for each carb and run them side by side. I think you can tape the tubes to a piece of cardboard.

Your carbs should first:

1) have slides mechanically sync'd
2) needles clipped in the same notch
3) jets matching & all clean
4) Air screws matching & at recommended turns

Then connect each side of a tube that's shaped like a 'U' to one of the manifolds to compare the vacuum of the two manifolds

Well I've gone through the carbs, and they're spotless. All jets match, everything moves freely, etc. The needles are snapped into the same position across all four, but I'm not familiar with mechanically syncing the slides...


And here's the setup I was using for the manometer. I've been told to construct them like this, but I've never had much luck.

I find it odd that all of the oil is getting sucked in right away then... Maybe you have nil compression on one cylinder, because even if it wasn't firing it'd still pump.

If it is built right, the fluid should stay balanced if the vacuum is fairly equal. A huge imbalance would be required to slurp the fluid up the hose.

If the mechanical alignment of the throttle butterflys is WAY off it might have one butterfly closed at idle. may need to redo the mechanical bench sync first to get them close.

That's an interesting layout. The others I've seen like this were made on a yardstick (3 feet) and had a restrictor (carb jet or the like) in each tube.

I'm thinking they may be way out of sync now, and so you'll need to bench sync them first to get them a bit closer. Should be more equal then when you vacuum sync them. Just do a search for 'bench sync' and you should find some topics on it. If you have a manual, its described there as well. I don't know anything about CV carbs, but the process on the VM carbs is pretty simple.

Also, when your bike is running (not hooked up to the manometer) are all the pipes hot. Just wondering if one cylinder is not running correctly.

The tubes need some sort of an in-line restrictor, or the fluid will be sucked out. Both of my old-style mercury sync tools have them in there.

Restrictors can be simple, from a small clamp to a jewelry bead in the hose, or I've heard of filling the hose with hot glue and pushing a needle through the glue to make a hole.

A piece of wire may be too large too bench synch the butterflies. Use your eye to get a whisker of light between the butterfly and throat.

And the 750 CV34 carbs can be synchro'd doing two at a time with a two hose manometer. There are 3 synchro screws; between 1-2 and 2-3, and 3-4.
1 and 2 are done together, then 3 and 4. Then hook 2 and 3 together and set them equal.

restrictors are needed for sure - my factory set came with them too. Find something that will fit in the tube and make sure all 4 are equal, whatever you use. I think mine are short pieces of hard plastic tubing that fits tightly into the hose and still allows a small amount of vacuum to pass. Keep us posted - I like your hand made manometer!

Spend the $60 on a set of gauges (4) and be done with it....
Better yet, $120 on a Morgan set, can't get any better quality than that for the money...

Seriously, I don't get this here or in other postings for as important/crucial it is to get your carbs dialed in for optimum operations, why not just buy a set of vacuum gauges designed for this function.

Maybe I'm missing something but I truly don't understand this logic... :S

OMR