Jetting Info on KZ900 - Help!

I tore down the carbs today to get an idea what I have in this 76 kz900.

The id tag on the carbs say "120" and a "1" right below it.

Main 140
Pilot 15
Needle 5CN29

The carbs run ok, but not so great around 4-5k, then open up fine. I also have some new carb holders coming because mine are leaking - I thought I should go ahead and replace all the rubber and address the carbs at this time.

The bike has pods and a V&H 4 into 1, stock ignition. The rest is pretty much stock from what I can tell.

I assume after 30 years, someone knows where a good starting point would be. From what I have read, the 140 sounds large, but sounds like it depends on the carbs I have. Not sure .. can't find any posts where people address the '120' tag. Are these stock ?

Thank in advance for sure.

Post edited by: thetemples, at: 2006/08/20 23:20

Hey there Temples. Check out Wired George's site at wgcarbs.com and you might get the info you need relatively quickly.

He is the resident carb expert at Kzr and he certainly knows the 900/1000 carb lineup.

Cheers-Colin Firth-Ontario Canada
1977 Kz650 Custom with 14,000 original miles. Newest incarnation has Wiseco 810 kit with lottsa go-fast goodies.

Below are pics of the carbs. From looking at Z1 and wiredgeorges web site, I think I have stock 26mm carbs. And if thats the case, my jets are all wrong.

Z1 Seems to recommend 115 main and 5DL31-3 on the needle, 17.5 on the pilot.

Do I seem to be on the right track?





Post edited by: thetemples, at: 2006/08/20 23:20

Chris, look down on the bowl side of those carburetors and see if there are pilot fuel mixture screws located at the back of the bowl on the engine side. I think they are Suzuki VM26 carbs of some sort but some of the other things mentioned don't quite match my records for those carburetors.

Yes, there are mixture screws on the bottom side of the carbs on the engine side as mentioned. Those threw me for a loop when I saw those. Are these totally the wrong carbs for this bike?

I am pretty sure they are either off a 70s vintage GS850 or GS1000. I tend to get those things confused in my mind and will eventually have to do some documentation to get them straight. Somebody has rejetted them (quite inappropriately I might add). The Suzuki carbs are a bit harder to tune and usually run leaner than Kaw versions of the VM26 but they will work if you can figure out how to tune the idle circuit. With pods and aftermarket pipes, probably use around #110 mains and #17.5 pilots and clip the jet needles to #4 slot if they have slots. It is critical to replace all orings on those carbs in order to get a smooth idle and start with the air screws and mixture screws out about 1.5 turns from LIGHTLY seated and then start adjusting if the idle needs adjusting. To judge, see how the bike pulls away from a dead stop... if you must slip the clutch a lot, turn the pilot mixture screws out 1/4 more and repeat till it accelerates away from a stop cleanly.