Kz900 won’t rev over 3k

[Nick.s]

No not really, I just want to know if the bike will rev past 3k, it doesn’t matter if it runs smooth or not.

[Nick.s]

At last I’ve got to the bottom of my problem, after fitting a borrowed set of carbs from Gus the bike ran ok. On inspection of my carbs I found the pilot fuel screws were in too far, I’m not sure how this happened because I set them to 1 3/4 turns out. The problem was that the tick over was too high so I turned the fuel screws in 1/4 turn which slowed it down ( not enough fuel at high revs I presume) but two of them were almost completely closed.
how do I set it up so that the revs are low enough to start with?
The jets are 112.5 main and 17.5 pilot. I’m not sure which notch the needles are on.

[zed1015]

Don't use the fuel screws to adjust the idle.
Fuel screw is only for pilot mixture setting.
Having the fuel mix screw almost closed would have caused pilot starvation, this would not cause a fuel shortage at high revs but a flat spot that the engine may struggle to pull through.
Start with the fuel screws 1 and 1/2 turns out.
Jet needles in middle position.
Main jet size will most likely need to come back down
Make sure your slide adjustment screws are half way along their threads other wise you can run out of idle adjustment.

[Nick.s]

Ok, thanks for that, I will give it a go this week. I’ve got the slide gap set at 0.8 mm (engine side) and the pilot jets set at 1 1/2 turns out. It was set like this the first time, but the revs were too high, and the throttle stop was right off.

[chrisw1]

This may be useful

http://www.aloh.co.uk/renovation/

[zed1015]

Ok, thanks for that, I will give it a go this week. I’ve got the slide gap set at 0.8 mm (engine side) and the pilot jets set at 1 1/2 turns out. It was set like this the first time, but the revs were too high, and the throttle stop was right off.

Yes! sounds like the slide adjusters were set on their limit.
Pull the tops off the carbs.
Wind the throttle stop to lift the slides around 3mm and then drop them shut on the adjusters.
This will enable the throttle stop screw to control idle.
When vac balancing the carbs, try and sync to the carb with the lowest reading.
This will prevent the adjusters going toward the wrong end of their limit again which is the cause of your troubles.

[Nick.s]

Ok I just did that, I wound the stop down about 1/8 inch and set the slides to 0.8mm which gives me chance to drop them down. Also I found the needles were on the lowest setting so I put them in the middle, I will put in the 102.5 mains tomorrow.

[kev edwards]

Just going through my carb info for a 900 with 26mm carbs and main is 115, pilot 17.5, needle 5dl31 on 3rd groove, pilot screw 1&3/8 out +- 1/4, and 22mm float level

[zed1015]

Nicks carbs are Z1000's though.
105 is stock main for A3/A4 etc.

[kev edwards]

Nicks carbs are Z1000's though.
105 is stock main for A3/A4 etc.

I only posted this bearing in mind the airbox differences, so I guess his final set up could be somewhere in between.

[Nick.s]

Ok quick update, I changed the mains to 102.5, fitted new needles and set them to middle position, set the slides and set the pilots to 1 1/2 turns out. I just tried the bike and guess what? It’s the same!!! Although now I can keep going and it seems fine after about 4k revs, so it’s just hesitating for a while then works through it. So is this just a setup issue now? Or should I bin the carbs a get different ones?

[zed1015]

Ok. Sounds like you are getting there.
Now to figure if you have a lean or rich condition causing the hesitation.
Take the bike out and feather the choke (enrichener) at the point of hesitation.
If the running improves you have a lean condition, if it makes it worse it's too rich.
Looking at the slight improvement you had with the smaller mains it could be that you need to go down to 15 on the pilot and hopefully the choke test will confirm by making the issue worse.

[Nick.s]

Ok will try that when I can.
Thanks for all your help you’ve been great

[Nick.s]

I finally got fed up with these carbs and got a set of standard carbs for my bike, there were lots of parts missing from them but I had all the bits I needed on mine. So I swapped all the parts over to make a good set, but when I fired it up it wouldn’t run properly because it was over fueling. I then noticed the needle jets were missing which I hoped was the problem. I got a keyster carb kit with the needle jets and built them up again, all bog standard, also changed the oil and filter because it was smelling of petrol.
Anyway I fired it up yesterday and it runs lovely, ticks over no
problem. All I need to do is road test it when this storm blows over.
So fingers crossed, thanks to all especially Rob and Gus.
Cheers, nick.

[Indie500]

Hi Nick, I have the same problem so this thread is really interesting, I've done all the things you have tried and still the same, big flat spot at 3k. I also had the choke plungers re sealed by Rob Meggit (search him out on Facebook) but no change. Hope you keep the thread going and ill let you know how I'm getting along as well..