Carburettor Help

[Arctic Fox]

https://photos.app.goo.gl/zqWzDGjJijoz5YPR9

Found on my A4, any idea what they are? How do you identify them? Trying to identify as a replacement jet clashed with the emulsifier tube. Now don't know if its the jet or tube that is wrong.

I found a diagram with VM29 smoothbores on a KZ900 where the carbs, linkage and peripherals look very similar, however I'm told they are not those. Alsp now know the black cover should be a vent pipe.

The bike was originally 1st registered in 1975 in Isle of Man.

[warren3200gt]

Mikuni Vm26ss or vm28ss?. Need to measure the throat diameter to tell.

[Ultim8pc]

Mikuni Vm26ss or vm28ss?. Need to measure the throat diameter to tell.

Would agree, they are not 29mm smoothbores though.

[ZedHead]

Found this...

I think it shows Z1000 A1 VM28's with the pilot screw in the float bowl and no air screw.

viewtopic.php?t=11981

This would suggest that Arctic fox has a set of Z900 VM26ss. However, here is the issue...

They are fitted with Mikuni 258 series needle jets (top), that were not standard in Z900 A4 carbs. Not the correct 243 series shown below. Hope this helps

[kev edwards]

I have a 26 set in front of me and the inlet throat has a thicker wall where they have not been machined out as much as Fox's, i would say the are 28's you have there.

[Arctic Fox]

Measured the throat on a couple of them, it is between 28.5 and 28.6mm diameter. So that is one conundrum resolved.

[warren3200gt]

It's the measurement by the slide that counts.

[kev edwards]

Measured the throat on a couple of them, it is between 28.5 and 28.6mm diameter. So that is one conundrum resolved.

Yes that's about right for 28's.

[Arctic Fox]

Just spent a while looking at various images, could they be VM28 parts from a Type 1 Z1R?

Couldn't directly measure the diameter by the slide, putting a steel rule in there that is 26mm wide it appears to be 28mm, certainly not 26.

[Philippe]

Hi Arctic fox
based upon the pictures I would say it's the third carb and it's a Mikuni VM28SS. The black rubber shouldn't be on the copper tube. The copper tube is connected by a rubber hose to the vacuum fuel tap.
You have to look for a number embossed in the carb slide. If you found that number you can identify the type of bike it was on originally. My guess: a Z1000ST or Z1000MK2, the carbs are very similar, only the main jets are different.
Good luck
Philippe

[Arctic Fox]

Thank you Philippe,

https://photos.app.goo.gl/tiWSnHqrKJ4AN4wWA
is a picture of slider, it says 1,75 I believe. Is that what you meant? And yes it is number 3 pictured.

I got the bit about the rubber, is a vaccum fuel tap necessary? I don't think I have one! They were (mostly) just left open when I got the bike. Figured I'd just run some pipe up under the tank when I put them back.

[Philippe]

Hi Neil
thanks for the picture, it is 1.75 indeed. I'll check it out, I don't know it by heart but I think it's Z1000ST, not sure yet so wait.
On your Z900A4 you don't have a vacuum tap but a "normal" one. On the N°3 carb you have to leave the rubber on when you mount them. If you don't, the mixture in the third cylinder will become too lean because air is sucked in if you remove the rubber resulting in a very hot cylinder with all the consecuenses you don't want.
I don't know how the carbs were originally mounted on your bike because the VM28SS carbs have one central T between the second and the third carb and connection pipes between the first and the second carb on one hand and between the third and the fourth carb on the other. The vacuum tap has one drain pipe as an A4 tap has two drain pipes.
As for rubber hoses, they are mounted on the second and on the fourth carb and provide an escape for the air in the float chambers. You can bend them a little bit downwards and leave them under the fuel tank.
Talk to you later this evening.
GrtZ
Philippe

[Philippe]

Hi Neil
I'm back. I checked it, 1.75 is the cutaway of the Z1000ST carb slide. So if you want to refurb your carbs, you'll need the refurb kits for the Z1000ST. As far as the main jets are concerned you'll have to decide which one you'll need. That depends on the exhaust system. I have no experience in changing the main jets because I rebuild a bike to standard. I never used z1000ST carbs on a Z900 A4. I think someone here can tell you what to use.
GrtZ
Philippe

[Arctic Fox]

Thank you Philippe for your help, its been a challenge! Thanks for the advice.

2 - 3 are connected with a Tee piece, with the 'third' port blocked off.

Exhaust is Harris 4 into 1, although I may put the original 4/4 back on. Any advice on jetting appreciated. In the KZ900 Motorcycle Shop Manual they suggest VM28SS were fitted as standard (Z1F-32818 on), Main Jet 112.5, Air Jet 1.0, Needle Jet 0.8, Jet Needle 5J9-2, Pilot Jet 17.5, is this a good place to start?

[ZedHead]

Hi Arctic fox
based upon the pictures I would say it's the third carb and it's a Mikuni VM28SS. The black rubber shouldn't be on the copper tube. The copper tube is connected by a rubber hose to the vacuum fuel tap.
You have to look for a number embossed in the carb slide. If you found that number you can identify the type of bike it was on originally. My guess: a Z1000ST or Z1000MK2, the carbs are very similar, only the main jets are different.
Good luck
Philippe

Good call Phillipe. I didn't realise until now that MKII engined bikes went back to air screws instead of the under bowl pilot screws of the Z1000 A1/2 carbs. So this makes sense.

I understood that the fuel tap vacuum came from one of the inlet rubber vaccum points? I think the nozzles in this case are for breather pipes?

The number stamped on the throttle valve slide refers to the cut away in multiples of 1/16 inch. Non US spec being 1.75