Z900A4 low speed issues

[sprint]

I have a UK std build Z900A4 which is an absolute pain at low speed and coming off a closed throttle where it stutters and stalls before picking up.

It ticks over without any problem at 1000 rpm and above 2K picks up and runs without any problems, but if you close the throttle and then open it again it will stall and stutter until the revs get above the 2K rev region when it will be absolutely fine. Carbs are balanced and I am using NGK B8ES plugs. Carbs have been stripped and cleaned, together with the jets, numerous times.

Any suggestions as to what the cause is and any potential solution(s)?

Thanks

[MrDavo]

Float levels? Cheapo pattern float valves? Genuine ones are very expensive, but made a huge difference when I couldn't set the levels properly.

Correct pilot jets? needle position?

[zed1015]

Try feathering the choke as you hit the stumble.
If it starts to pull clean you need a little more fuel off idle and if it makes it worse or no difference then you may have too much fuel.
You should be able to tune it out on the fuel mixture screw.
Before that you should also check that the ignition advancer moves freely and isn't sticking.

[warren3200gt]

A mate had a similar issue on his A1. Just couldnt resolve it. Out of desperation he asked on a H**** forum as everything that was suggested on kawasaki forums just didnt resolve the issue.
He was advised to link the vac ports on carbs 2 & 3 and likewise with 1 & 4. I dont understand the mechanics behind it or the theory as why it should work but it did like a dream. All it cost was a bit of tubing and a few clips so cheap to try and nothing lost if it doesn't for you.
If anyone can explain why that should work please explain or even whats happening if you do this !

[Al]

Before that you should also check that the ignition advancer moves freely and isn't sticking.

There is a tiny thin shim immediately behind the cam on the baseplate. It breaks and can jam the mechanism.

Is it on points or electronic ignition of some sort??

AL

[sprint]

Thanks for the replies.

Bike has std floats which have been set with a manometer so levels are OK. It is also fitted with electronic ignition.

It also has the correct needle position and the correct pilot jets fitted.

Will give trying the choke and see if it makes any difference. Pairing the No 2 & 3 and 1 & 4 manifolds is intriguing and something I can try as there are already stubs available for doing the carb balance and only requires a bit of tube connecting the appropriate manifolds.

[Freebird]

I had a very similar problem with my Z1000, I followed all the carb advice to no avail too.

In the end, I found the ignition advance springs were too stiff. I replaced them and it cured it for me.

[Mr Bump]

If it turns out to be a rich spot fouling the carbs could it be the condition of the choke plunger rubbers? They can harden and split. Zed1015 does a very good exchange and repair service.

Gpz750 uni have those pipes connecting the carb pairs as factory fit. Obviously there for a good reason. I figured they might take out some vibration by balancing the carbs a bit or something but maybe they have more effect than that.

Olly