I recently ordered a set of carb rebuild kits for my ‘78 Z1R and I purchased the wrong kits. I should have researched the numbers stamped on the carbs before ordering. The carbs have Z12 and 00 stamped on the motor side mounting flange. Did the factory ever use these carbs on 77-80 Z1R’s? From a first glance it appears the bowl gasket is the only thing I can use here. Also, the idle mixture screw has the threads at the top just below the head and is much shorter.
Been rebuilding the mikuni vm carbs for decades and never once needed a rebuild kit. They are a waste of money and the jets in those are not mikuni so the sizes are not correct. Send them back and reuse what you have after a good cleaning of course.
The following user(s) said Thank You: 650ed, Nessism
Some photos of the carbs would be useful. For a '78 Z1R they should be VM 28 SS carbs. You can tell if they are 28's by measuring the outlet throat...it should be a tad over 28 mm.
If they are still stock they should have:
107.5 main jets
5CN15 jet needles in the middle slot (3 of 5)
1.5 mm cutaway (on the bottom)
O1 needle jets
Probably the best way to tell is to check a jet needle.
Most of the brass parts should still be good, as they don't wear much with only fuel or fuel/air going through them. The main parts to change are the o-rings and gaskets. I also like to change the needles and needle jets because they wear from the constant action of the needle going up and down inside the jets while air is rushing through the throat. The only aftermarket kits I will use are Keyster. You get a lot of stuff you don't really need but you do get the needles and needle jets.
I have a couple of Z1B's restored, an '80 KZ1000LTD restored, a 1981 KZ550 restored and a 2008 KLR 650 for off road fun. My wife has a 2019 Suzuki DR 650 for on and off road.
I reuse all the brass too. Main possible exception is the float needle and seat if there is a lot of wear and the spring in the needle can't hold up the weight of the float. You can get real deal Mikuni float needles and seats for decent prices off Amazon. Do some research first to find the proper part number and then go hunting.