KZ900 carb help

[1975-S1C]

Todays presents from the postman included 4 Keyster carb kits courtesy of the good folks at Zpower. Gotta say, Zpower send stuff out really quickly, super happy with that.
For the sake of folks following this thread I’ll post what I find, along with my dim questions !

A brief recap.
The choke plungers went off to Rob for new viton seals. I don’t know how bad these look (4 picture cluster) to those with more experience. At least they have now been ruled out, both now and for some time to come. As you can see they came back from Rob looking all shiny and new.

[1975-S1C]

Moving on to today.
I didn’t get the chance to actually attempt to set the fuel levels, but I did manage to get myself all set up ready with the carbs bolted to a spare piece of lumber and clamped upright in the vice, and being fed from an auxiliary tank as you’d expect.

[1975-S1C]

I am planning to only use the Air Screws (with new O rings and springs) and the fuel inlet needles and seats from the carb kits. I’m interested what people think about potentially using the other bits (main and pilot jets in particular) from the kits versus retaining the original ones ?

Anyways, I changed out all of the Air screws and needles and seats in readiness for the fuel level work to start tomorrow. Got to say, the Air Screws (4 picture clusters) in particular looked pretty ropey compared to the new ones from the carb kit pictured below. The Air Screws seals are shot, they are worn away and / or compressed to a flat profile instead of round profile so probably not making a great seal. Also the needle areas of both the air screws and fuel inlet needles are pretty bad.

[zed1015]

I am planning to only use the Air Screws (with new O rings and springs) and the fuel inlet needles and seats from the carb kits. I’m interested what people think about potentially using the other bits (main and pilot jets in particular) from the kits versus retaining the original ones ?

Unless they are physically damaged there is no reason to replace the original jets.
That being said i have used the entire contents of Keyster kits to change the spec of these carbs when i have bored them out from 26mm to 30mm etc and they have performed flawlessly.
I will only ever use either Genuine Mikuni or Keysters parts in these VMs.

[1975-S1C]

Good to know. Thanks Rob.

[1975-S1C]

For completeness, these were the compression readings I got with a cold engine, full open throttle and about 6 kicks on the kickstarter

[zed1015]

For completeness, these were the compression readings I got with a cold engine, full open throttle and about 6 kicks on the kickstarter

Plenty good enough and the variations between cylinders are all within limits.

[1975-S1C]

Ok chaps, a little more help please.

Tried setting the fuel levels this afternoon. After 2 hours of fiddling about I’ve got precisely nowhere !
At first I tried just bending the tang a tiny amount at a time, without any real science behind it. That was so hit and miss that it was driving me bonkers. Too much, then too little. Aaaaaargh
I then decided to gradually move the tang using my feeler gauges so that they just went under the tang, and used them to open the gap a measurable amount at a time. This proved to be better, but still the damn thing refuses to play ball.

How long should it take for the correct level to be reached ?
I was expecting a bit like a toilet cistern after it’s flushed, I.e. it fills quickly then shuts off fairly quickly at the correct level.
If I set the tang so that it shuts off abruptly it gets nowhere near the correct level (way too low). However the difference between that and it overfilling is tiny, albeit that it takes several minutes to gradually creep up to being overfilled.
I thought with new fuel inlet valves and seats that this would be a fairly easy task, albeit a bit iterative., but it has proved rather frustrating so far.

I’ve packed in for the day and am off for a curry and a few beers.

As always, your help and suggestions are welcomed.
Cheers
Paul

[warren3200gt]

Check the float hinge plates aren't bent and the floats aren't bent.
They were as the solid circle when new.

Screenshot_20240108_220602.jpg (32.94 KiB) Viewed 2473 times

[r3sc]

How high have you mounted your auxiliary fuel tank? Too much head could give you odd readings.

[1975-S1C]

How high have you mounted your auxiliary fuel tank? Too much head could give you odd readings.

Hi r3sc. There’s a picture a few posts back. Does that look ok ?

[1975-S1C]

Check the float hinge plates aren't bent and the floats aren't bent.
They were as the solid circle when new.
Screenshot_20240108_220602.jpg

I’ll double check tomorrow Warren, but I think they are pretty aligned.

[r3sc]

I always try to mount it so that it’s approximately the same height as the tank would be in normal use. When balancing I hang the tank on the bar end or mirror.

[ADRIAN H]

I always try to mount it so that it’s approximately the same height as the tank would be in normal use. When balancing I hang the tank on the bar end or mirror.

Totally agree, if it's too high can cause the float valve not to close, and you get overflow

[1975-S1C]

I hadn’t even considered the height of the auxiliary tank, but in reality it’s actually about 5 or 6 times higher than the tank would be in normal use.
I will rectify this tomorrow and give it another go.
Thank you.