Z1 Carb Sync Problems

Several people have stated that the original Z1 carburetor design (28mm Mikunis) was problematic even when new. The synchronization screws were mounted on a set of individual shafts and there seems to be a lot of play in the armatures. When the engine is revved even slightly, the sync changes. If the engine is revved hard, the sync is completely lost.
After tiring of regularly synchronize, I swapped them for a very good set of 26mm Mikunis from a 78 or 79 KZ1000. The later KZ carbs are supposed to be of a more reliable design. The new carbs were cleaned, fitted with new parts (112.5mains, 15 pilot), float level was checked @26mm, and the airbox squeezed into place.
The bike started right away, idled a little high, but ran ok. The new started to sych alright, but the idle kept increasing to roughly 3K rpm. The idle screw was backed out all the way, and both throttle cables removed. The bike still idles @ 3K.
Is it possible to reduce the height of the slide to bring the idle down? Sorry for being so long winded but I am really at a loss…..

Thanks!!!

hey dude!
first thing is phyiscialy looking at the throttle blades. take off the carbs and look at the baldes, the gaps should be the same as near as you can tell. open the throttle and watch (be sure to pull in the right spot) they should all stay even both opening and closing. also check your throttle slides. from the back look in and with a scribe lift the slide up and realease, the slide should come back down slow and easy. when i got my kz i took of the carb and checked my sync. they had the left and right pairs linked together wrong. they should be mechanicaly acuated and spring realeased. it takes a special tool and prochedure to sync completly, and a carb with the idle circut off adjustment throws sync off at idle so its very complacated, but setting with a feeler gauge can be a good start. good luck... joe

Once the bike is warm, the lowest it idles is 3K rpm without the cables attached? Is that correct? OK, if it is, first thing is to check to see if there is a vacuum fitting on the carbs. The 79 carbs came with an accelerator pump so you must have 78 or earlier 26s since you didn't mention a pump. I don't believe the 78 or earlier carbs have a vacuum port which will be located on the side of the #3 carb in the same position as the vent fittings on #2 and #4. If there is a vacuum fitting, cap it unless it is connected to a vacuum petcock.

OK, if there is no vacuum fitting, you need to take the carbs off and bench sync them. This is the purpose of the bench sync... to get the slides to move up and down in the center of the range of the idle adjust screw.

* Take off the tops.
* Loosen the sync screw locknuts.
* Back out the idle adjust screw then tighten it to where it is just contacting the bellcrank (the bow-tie shaped thing that keeps the ends of the throttle cables).
* Tighten the idle adjust screw just a bit so that the slides just start to raise.
* Observe the slides on the side that connects to the cylinder head. Turn the sync screws in so that you shut all four slides.
* Adjust the gap between slide and venturi so there is an eyelash of opening. Just do it by eyeball or you can use a very fine wire. The eyeball method is probably just as accurate as the wire.
* Test the idle adjust screw to ensure that the slides shut all the way and will open to where about 1/16" is visible between the slide and venturi - leave it there as that is about the amount of opening needed for a correct idle speed.
* Put the carbs on your bike and warm the bike and sync with vacuum gauges.
* Tighten locknuts on sync screws and replace the caps on your vacuum fittings.

This procedure will get your bike idling in the proper range using the idle screw.

Thanks for the advice!