KZ900 carb help

[Gray17]

Hi Paul, for what its worth i found exactly the same thing when i attempted to my own float heights, again like you thought it down to poor sealing on the float valves, again like you replaced all with brand new Keyster kit, thinking this would solve the issue, alas mine like yours kept either not filling to correct level or overflowing. Its a very hit or miss affair, or maybe novices dont have the nack. I do like your idea of using diff thickness feeler gauges to bend tabs hadnt even considered that, but gives you a measurable amount of bend on tab. After rebuilding all of my engine the only thing remaining is the carbs to fit, but held off to see if i can follow your process to success, their not easy getting on and off and the more times you do it the more risk of damaging the rubbers. I too hadnt considered tank height as reasoned a full tank heavier then a partial filled therefore a higher with only a small amount is equal pressure. Have to say they are very tricky to get correct and having to leave a while between each adjustment to see if level does indeed shut off rather then creeps up doesnt help. The only consolation is with weather the way it is at mo dont feel im missing out riding it as too wet!
Do hope you get it sorted, as hoping your post will help me, great photos by the way.

[1975-S1C]

Thanks Gray.
Glad it’s of use to you too.

I’m going to a bike show in a bit on my S1C, but am planning to take another look at the carbs later and will report back then. I’ll be taking on board the advice from r3sc and Adrian and will make my set up as close to reality as possible.
I’ll also double check my floats are all properly aligned as Warren suggests.

One more question I have is, how long should it take for a carb to fill from empty to the correct level ? Should it fill and cut off fairly quickly ? Or take several minutes to finally reach the level ? Maybe I will know more on this when I’ve changed my set up and tried again, but any thoughts / insight would be gratefully received

[Gray17]

I assume your asking everyone, rather then just me, but my own experience of carbs was very much like yours in that even with all new components fitted, all floats checked for allinement and flat, i could set a height that seemed to work, however if i left it for a while one of the carbs would start to overflow, but this was very random, as not always same carb, or at all. sometimes it would flow straight away, other times after several mins or never, it was also effected if on main or canted over on lazy stand. In my case proper fuel tank was used only difference was fuel quantity, worst when full then half empty. My conclusion like yours something not quite right but couldnt see what? However with other issues on mine present i decided a strip down was needed so carb issue remains, hence why im so interested in this post. The thing is though lots of people on the forum do this regularly and have no such issues which leaves me to believe its either my method or lack of nack thats at fault rather then the components themselves? However judging by the numerous posts relating to bad running and carb related issues theres a lot that suffer similar problems and struggle to get it cured once and for all.
In my case Nigels excellent carb setup guide didnt help, hence why i think its my method thats wrong. Its also why i read these posts with such great interest, the more you read the more you learn!

[warren3200gt]

The float needle is not an on/off switch, they were never designed to be that just to regulate excessive fuel supply. They all leak by to some degree. If they were you wouldn't need a fuel tap, either on/off or vac or an overflow port.
Things that affect the float needle seal are many but worn needle/seat, dirty needle/seat, micro crap in the fuel lines, float condition,, adjustment, and trueness to original position and a not overly bent tang so that the needle slides straight up the seat and isn't trying to be forced in at an angle. Also feed height of the remote tank.

As a result of the never having been designed or working as an on off switch if you leave the feed open for long enough they will dump fuel out the overflow. They don't overflow whilst the motor is running as fuel is consumed by the engine faster than any leak by could replenish.

[kev edwards]

I have always, lapped the valves and seats in, also some of the needles are a little snug so I rub the ribs a couple of times on 1000 grade, I also don't think the height of that little bit of fuel will create enough pressure to cause problems.

[1975-S1C]

I had just over an hour in the garage earlier.
In that time I managed to not only change my set up, but also get two carbs set up pretty good. Hallelujah !

I checked the floats and they were nicely aligned. Also measured the distance between the inside edge of each of the two floats all the way around the circumference and they were consistent.
Then I changed my set up so that the auxiliary tank was about the same height above the carbs as it would be on the bike.
Rather than guessing how much to bend the tang, I used my feeler gauges as before. This seems to work well and allowed me to home in on the right setting a little at a time.

With the fuel tank lower the results are much more consistent and repeatable. Not only that, it achieves the correct level fairly quickly and the needle seems to stop the flow pretty much completely.

Here are the results for the first carb.
I’ll post the rest tomorrow.

[Al]

After you turn the fuel tap on any movement of the tube will give a wrong reading. Particularly lifting it either up or down. If it slips down and you lift it back up again you need to drain a bit out or start over. Bending it with the thumb will have a similar effect. I set mine a little low, perhaps where yours in the picture are now. They will creep up a little as the float needle and seat become friends and the needle plunger spring looses its initial youthfulness.
Youre doing the right things the right way and its not as if you will need to do it again in six months, just as well as its a proper faff. I do mine on the bike with the engine running at idle. Knowing i will not get it right first time and they will need to come off again i dont fit the airbox. Just run it without for the duration. I have also been known to bend the tang the wrong way and add two operations to the four it normally takes to get it just right.
Doing it running at idle gives a whole host of information about re-charge rates and you can see if any of the floats are sticking shut or reluctant to close. Its another level of complexity but once you get used to it its just as easy as any other method. You can show what its doing dynamically and turn the engine off and see if the level creeps up. Etc etc etc.
Keep going.
AL

[1975-S1C]

I was holding the pipe alongside the carb when I opened the fuel tap Al.

I’m feeling much more confident that I’ll be able to get the two remaining carbs dialled in now.hoping to do that in the morning. More results to follow.

As always, I appreciate the advice from everyone.
Cheers
Paul

[1975-S1C]

Carb 2 done.
Perhaps a little higher than the level I was shooting for, but after the amount of faffing involved to get it like this I’m gonna call that for the win !

Just the other two carbs to do, possibly this evening as Summer seems to have come to an end (not that it ever really got started anyway).

[Al]

I see you have a lot on your plate but if you happen to have a measuring stick in your hand as you move through the bank of four i would be very curious to know what the float level of one of the 'set' floats is. Its just curiosity for me but this comes up a lot here and never an answer as to how near the mythical '26mm float height',... a perfectly adjusted one is. I am sure there would be plenty who want / need to know for their A4's and for the range of VM carbs generally.
AL

[1975-S1C]

Good point Al.
I will put my vernier on the 3rd and 4th carbs and see what they measure. Was hoping to have done these this afternoon but didn’t get chance. Will have a little look later on.

[1975-S1C]

These levels look a bit more like it.
I dare say number 3 could benefit from being just a smidge lower, but I think we are pretty much there.

I didn’t open up 1 and 2 again to measure the actual float heights, but on 3 and 4 they were both at 28mm.

[1975-S1C]

Unless anyone has any suggestions on other things I should be doing whilst I have the carbs on the bench, I think the final 2 carb related jobs are:
- sync the carbs
- lube the throttle cables

I know I’ll need to re-sync the carbs on the bike once it’s up and running, and for that I’ll need to invest in a set of gauges. In the meantime I don’t have a scooby how to do it on the bench, so that’ll be tonight’s reading !

[kev edwards]

You can bench sync two ways, the regular is using a drill bit in the carb throats making sure they are all the same height, I take the tops off the carbs, and raise the slides via the idle screw, I then use a vernier and measure the height of the slides then adjust as needed, it's also advised to set the adjustment screws at mid travel first., this will put you somewhere near to where you need to be.

[Al]

I didn’t open up 1 and 2 again to measure the actual float heights, but on 3 and 4 they were both at 28mm.

Thankyou.
I did a bit of reading today and looked up the float heights and fuel levels for the VM26ss used on suzuki's; 750 / 850 / 1000.
To keep it simple the GS1000's use a float level height of 24mm and a fuel level of (averagely) 4mm, so not really a great deal of difference there.
Naturally some of the jets / settings / and needles are different to the Z12 00 Kawasaki carbs and so i guess this means that applying 900A4 parts or settings may be a problem if these carbs are used.
The only issue i could forsee (small chance) with the floats coming out at 28mm is that the 'limiting stops' may come into play a little early and prevent the float needles opening far enough. Recharge may be a little slowed perhaps. It may be that someone previously found it easier to bend the floats at the brass hinge than adjust them at the tangs!
I only mention it because a couple of years ago, after replacing some float needles (not in VM carbs) i ended up in the ridiculous situation where the floats would neither open correctly nor shut off properly. That was caused by me but also a pecularity of RS carbs that have a 'cast in' stop in the bottom of the float bowls.
Thanks again. I may be usefull for anyone; base setting the float heights and then thinking they have gone mad when they read the actual fuel heights.
AL