Kz900 won’t rev over 3k

[Nick.s]

I haven’t checked for air corrector jets, what do they look like? Would taking the air filter out correct it if there are correctors in?

[needaz1100r]

Don't go changing mains until you have sorted the 3000rpm issue.
There is no std main jet size for 1000 carbs and 4/4 pipes but 102 won't be far off for a 900 it all depends carb spec ,exhaust type and intake flow.
Stock mains on a GS1000 with VM28's is only 96 ( and the same 96 main for the Katana 1000 with 32 smoothbores )
112.5 is the average main on a stock Z1000.
There's no need to start changing settings that don't relate to the problem you have.
You wouldn't go buying specs because you are going deaf would you..

Also check the carb mouths for air corrector jets..
If the carbs have previously been run with pods on this bike or another then they may have the corrector jets still fitted.
This will also cause the bogging you describe due to over fueling with the airbox in situ.

Hallelujah! How many times do you hear, I changed the exhaust, took the airbox off and now it runs rough, do you think it's the ignition or the tyre pressure?

[zed1015]

There are no corrector jets in those carbs so that's not the issue.
Have you been through everything I listed in my first post.

[Nick.s]

I haven’t checked electrical fault under load, it’s got a new kill switch. Timing and auto advance ok, fuel ok. I set float levels when I overhauled the carbs, new coils.
The plugs get very sooty, in a very short time.
The only way I can rev past 3k is by feathering the throttle instead of just opening it fully, even then it only goes to about 4k
Would electronic ignition make any difference?

[zed1015]

That does sound like over richness or a restriction in the intake or exhaust.
You need to try running with the airbox off or filter out.
Also try with the baffles removed or a different exhaust.
I have had pattern 4/4 exhausts that kill the performance like this.
As for the ignition. I always junk the point and fit a Dyna 'S'.
They are night and day when it comes to starting and performance.

[Nick.s]

Thanks for all your help, I really appreciate it. I hope I’m not being too much of a nuisance.
I’ll try a few thing tomorrow, it does seem like it’s air related.
Thanks again
Nick

[Coose]

Well I’ve just set the valve timing properly, and checked the ignition timing. It’s still the same, all ok to 3 k revs then it splutters and won’t go any higher unless I back off the throttle then I can ease it up a bit

You did move the right cam, turn over the engine and then recheck the cam timing?

[z1bman]

what are the mixture screws set at standard base setting is 1 3/4 + or - 1/8

[Nick.s]

The pilot fuel screws are set about 1.25 turns out, I started at 1.5 but it was reving too high so I turned them in 1/4 turn.

[kev edwards]

For those carbs with that jetting 1and 1/8, but it is subject to a little variation, if the screws have been way over tightened before the holes will be larger and let more fuel through, do you have another set of carbs to try.

[Nick.s]

I have been offered a set to try, which I will when I’ve run out of other options. It’s odd that it will rev right up in neutral, but on the road it won’t. Seems like something is breaking down under load.

[zed1015]

I have been offered a set to try, which I will when I’ve run out of other options. It’s odd that it will rev right up in neutral, but on the road it won’t. Seems like something is breaking down under load.

If it's still on points have you checked the condensers.

[Nick.s]

No I haven’t checked condensers. How do I check them?
I’ve just tried it with no air filter and no baffles, it reverse up to nearly 4k, when I refitted them it went back to 3k. Number 4 plug looked brownish, the rest black.

[z1bman]

a good spark will easily jump a gap of between 7 -10 mm is the spark blue ? if its yellowish it is a sign of a bad condenser

[chrisw1]

I had the same issue when I finished my zed ....... back to the cam timing , you can have 28 links but both cams are 1 tooth forward if you know what i mean ........ I sorted that and it was fine