Where is my air Screw Adjustment

  I have a 1976 KZ900-A4 with original Carburetors ( I belive)  The engine runs a bit unevenly and roughly around 2,000 RPM. I’ve read that the 1976 KZ 900 models were modified to meet US emissions standards, and my bike is currently fitted with a #115 main jet and a #17.5 pilot jet.

To smooth out the running around 2,000 RPM, I want to switch to "European" specifications by installing a #117.5 or #120 main jet and a #20 pilot jet... This will likely result in a rich fuel mixture, so I’ll need to increase the airflow. However, I can't figure out where to adjust the air screw on my carburetors. Can anyone help me with this? I’ve attached some photos.

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Hello,

as i see, your bike is equipped with the  "later than original Z900"  , (K)Z1000 A1/A2 carbs, these carbs don´t have any air screws, they only have a fuel-mixture screw in the middle  underside, (head-intake side)
And i think also, the 20 pilot, and 120 main would made your mixture a bit to rich...just my 5 cent about...

Those 26's don't have an AIR mixture screw.
They have a FUEL mixture screw which is located under the carb at the front of the float bowl towards the inlet manifold.
This screw adjusts the pilot FUEL supply and is clockwise to lean off and anticlockwise to richen.


 

Here are some pics showing the difference between air screw and fuel screw paths.

I'd go full stock on the jetting.  Should be 107.5 main and 15 pilot, or something close.  Tune the fuel screw for best running.  Common setting range is from 3/4 of one turn to 1-1/4 turn, give or take.

From the photo your choke plungers are not seating down properly.  Be sure the plungers are able to fully seat or the mixture will be overly rich.

OK, sorry for that

MFP-Joe wrote:

Hello,

as i see, your bike is equipped with the  "later than original Z900"  , (K)Z1000 A1/A2 carbs, these carbs don´t have any air screws, they only have a fuel-mixture screw in the middle  underside, (head-intake side)
And i think also, the 20 pilot, and 120 main would made your mixture a bit to rich...just my 5 cent about...

    OK Thank you so much for the info I Kind of was hoping the Air screw was hiding under the brass ball, on the lefthand side (where normay they should be ) 

You have the KZ1000 VM26 carbs as have been mentioned. They had two different versions of those too. By looking at your pictures it seems you have the late 1977 and up because of the type of throttle cable holder shown. Be Super careful adjusting those Brass Fuel screws! If turned in too far you risk chance of binding the tip into the casting and it breaking off in that hole. Then you would be in a real pickle. Looks like someone had already been messing around with those, evidence the allen bowl M4 screws. 

thanks for the warning. I will pay attention to the problem. hope I can be able to regulate the some of the air on the fuel mix screw

thanks for the warning. I will pay attention to the problem. hope I can be able to regulate the some of the air on the fuel mix screw

Fuel screws will have no effect at all on the air. They control only fuel.

The goal is to have the correct ratio of air to fuel. Let's say you have a lean mixture of 15:1 and you want a richer mixture of 13:1. Lean means there is too much air for the amount of fuel, OR there is too little fuel for the amount of air. You can either reduce the amount of air OR you can increase the amount of fuel to change the lean 15:1 to a more usable 13:1. 

Your carburetors change the ratio by changing the amount of fuel. Other carburetors do it by changing the amount of air. The end result is the same.