bst 34mm air/fuel mixture

I have a set of bst34 carbs, was wanting to know what the factory setting is for the air/fuel mixture. How many turns in or out they should be????

IIRC those carbs have a forward lean to them. They were intened for bikes where the engine leans forward much more so than the KZs do. You may have issues with float / fuel height, as the bowl sits level to the ground on the forward leaning engine bikes. It most likely will not do so on the kz, and may lean to the back of the bike.

As to air/fuel screw adjustments here is some info for the carbs used on 86-88 GSX-R1100

Type: BST34SS
Main Jet: 130
Main Air Jet: 0.6mm
Jet Needle U.S: 5D29 U.K: 4D13-3
Needle Jet U.S: P-2 U.K: O-9
Pilot Jet U.S: 32.5 U.K: 42.5
Pilot Air Jet U.S: 135 U.K: 150
Pilot Screw setting U.S: Preset U.K: Preset (2 turns out)
Starter Jet (choke): 45
Float Height: 14.6mm (+/- 1mm)

Instructions on setting float height
To check and adjust the float height, carry out the following manner:

* Invert the carburetor body

* Gradually lower the float and observe the clearance between the float tongue and the end of the needle valve. When the tongue just begins to contact the end of the needle valve, stop lowering the float and hold it. Then measure the height (A) from the float chamber mating surface using vernier calipers.

Float height 14.6 +/- 1mm

* Bend the tongue as necessary to bring the height within the standard range

What ever the setting is,it is only a base setting. So why don't you start at 1 3/4 and with a hand held tach turn them in until you reach max rpm then back them off 1/8 turn.


You can't see the minute rpm changes with the bikes tach.


I know there will be a lot of people will jump all over this answer telling you the correct way to do it but this is basic tuning and you need to start some where and basic is expeident.

Thanks for the help guys

79kz1000* wrote: Thanks for the help guys

rule of thumb with air screws is that if you are achieving good engine behavior at idle and accelerating just off idle with the air screws set between 1.5 to 2 turns from seated you have good low speed jetting. If you have to adjust the air screws beyond the 1.5 to 2 turn parameters you need to possibly make a pilot jet change .