Z1 KZ900 Carb Identification & Specification
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https://web.archive.org/web/20120204062747/www.z1enterprises.com/reference/z1-carb-guide.aspx Z1 & early Z1-A Mikuni 28mm carbs
The early Z1 28mm carburetors are best identified by the combination of 17mm drain plug directly under the main jet, and the angular top cover held on with just TWO Philips screws.
With the exception of the early bikes, this style of carbs was on all Z1's and all Z1-A's up frame number Z1F-32817.
On the early Z1's are very similar carbs, but there are a couple of subtle differences. The carb body has less reinforcing ribbing - most noticeable in the smooth area in the main body, and very minor differences in the choke linkage. These carbs seem to have been fitted all the way up to engines in the 3000 range (Z1F-03xxx).
Late Z1-A & Z1-B Mikuni 28mm carbs
Part way through the Z1-A production run (After Z1F-32817), Kawasaki modified the carbs to help address performance / tuning issues with the earlier bikes.
The modified carbs are identified by a small drain screw angled to the side of the float bowl. Internally, the slide, needle jet and pilot jet were modified as well as the choke fuel pickup pipe placement. Not only did the drain plug change, but because the choke fuel pickup point changed, the float bowls between the early and late versions are not interchangeable. Externally, the carb linkages also changed.
In conjunction with the change of carbs, the ignition advance unit was changed as well - the advance unit previously ranged from 5-40 degrees of advance, and was changed to just 20-40 degrees of advance when paired with these later carbs.
KZ900 Mikuni 26mm carbs
With the release of the KZ900-A4 model in 1976, the carburetor design changed considerably. The size was reduced to 26mm, the body of the carb was totally redesigned. The top cover is more rounded and held on with THREE Philips screws. The float bowl retained the small drain screw design from the Z1B style carbs. Much of the design change was focused on smoothing out the raw power of the early Z1's into a more refined power delivery. These carbs tend to stay in tune better given the improved design of the synchronization linkage.
Mikuni 29mm smoothbore carbs
Once power-hungry riders realized the potential of the Z1 engine, a large array of performance parts appeared on the scene. One of the most important of these was the Mikuni 29mm smoothbore carbs. The stock carbs did not adapt well to the increased fuel demands of high-lift cams and high-compression pistons, nor the back pressure changes of the barely flow restricted 4-1 exhaust systems. The 29mm smoothbore carb was by-and-large a cure for many tuning problems. The top of the carb is identical to the 26mm (and later KZ1000 28mm) carbs. The float bowl went back to using the 17mm drain plug directly under the main jet. Great for racers as it allowed for quick changes of the main jet. None of the VM29's have an overflow pipe fitted in the float bowl.
lNote: some very early sets of 29mm smoothbore carbs have a float bowl with a small drain screw angled to the side.
Below is a reference of jet settings for the 29mm carb on Z1 / KZ engines. This is a good starting point for a bike with 4-1 exhaust, after market cams (up to 0.410" lift) and high compression pistons (approx 10.5:1). Each bike setup is different, so actual settings will vary.
We have included the Honda CB750 settings as a reference. You will notice the similarity of setup - so.... if you can find a set of 29mm carbs off a CB750, they should work on a Z1. The same is not so true with smoothbores setup for the Suzuki GS range. The slide cutaway is different (2mm) - yes, you can still buy new slides, but they are expensive.
28mm (VM28SC) Z1 & early Z1-A
Main Jet 112.5
Air Jet 1.0
Needle Jet P-8
Jet Needle 5J9-3 - last number is the clip position where 1 is at the top of the needle (leanest) and 5 is at the bottom (richest)
Throttle valve (slide) 2.5mm cutaway
Pilot Jet 20.0
Air Screw setting 1 1/2 turns out
28mm (VM28SC) Late Z1-A & all Z1-B
Main Jet 112.5
Air Jet 1.0
Needle Jet O-8
Jet Needle 5J9-2 (last number is the clip position)
Throttle valve (slide) 1.5mm cutaway
Pilot Jet 17.5
Air Screw setting 1 1/4 turns out
26mm (VM26SS) KZ900A4 & A5
Main Jet 115
Air Jet 1.0
Needle Jet O-6
Jet Needle 5DL31-3 (last number is the clip position)
Throttle valve (slide) 1.5mm cutaway
Pilot Jet 17.5
Air Screw setting 1 3/8 turns out
29mm smoothbores Z1 / KZ900 / KZ1000
Main Jet 120
Air Jet 0.9
Needle Jet O-6
Jet Needle 5DL31-3
Throttle valve (slide) 1.5mm cutaway
Pilot Jet 17.5 or 20.0 (or 25 in the later versions)
Air Screw setting 1 1/2 turns out
29mm smoothbores CB750
Main Jet 115
Air Jet 0.9
Needle Jet O-6
Jet Needle 5DL31-3
Throttle valve (slide) 1.5mm cutaway
Pilot Jet 17.5 or 20.0 (or 25 in the later versions)
Air Screw setting 1 1/2 turns out
29mm smoothbores KZ650
Main Jet 105
Air Jet 0.9
Needle Jet O-4
Jet Needle 5DL31-3
Throttle valve (slide) 1.5mm cutaway
Pilot Jet 15
Air Screw setting 1 1/2 turns out
