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Discussion Starter #1
I have an old Mikuni BNO carb, not the round slide but a butterfly controlling air flow. There are two carb adjustments on the outside, high speed and low speed, and one in the entrance to the throat. My question is when the high and low speed screws are opened, do they lean or richen the mixture? And what is that screw adjustment in the throat do.

Right now it is mounted on my 1974 cheetah with a 440 kawasaki. I think the carb came off a Chapparal. Anyway the engine starts with some effort, once started idles good, and runs smoothly up to 1/8 throttle (around 20-23 mph) then when I give just a little more throttle it takes off like I just gave it 3/4 throttle. It is very touchy throttle in that zone. I would like to smooth out the performance.
 

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The top screw on the right hand side is the High Speed Mixture, clockwise rotation of it will lean the mixture. Initial setting for it is 1 1/4 to 1 1/2 turns open from gently seated.

The screw on the left side by the throat is the Idle Mixture, clockwise rotation of it will lean the mixture. Initial setting for it is 1 1/4 open from gently seated.

The lower right hand screw is your Idle Speed.
 

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Discussion Starter #3
Thanks Old Man, I will start the carb settings as suggested and work from there trying to get the throttle smoothed out.
 

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BNO carb

I have an old Mikuni BNO carb, not the round slide but a butterfly controlling air flow. There are two carb adjustments on the outside, high speed and low speed, and one in the entrance to the throat. My question is when the high and low speed screws are opened, do they lean or richen the mixture? And what is that screw adjustment in the throat do.

Right now it is mounted on my 1974 cheetah with a 440 kawasaki. I think the carb came off a Chapparal. Anyway the engine starts with some effort, once started idles good, and runs smoothly up to 1/8 throttle (around 20-23 mph) then when I give just a little more throttle it takes off like I just gave it 3/4 throttle. It is very touchy throttle in that zone. I would like to smooth out the performance.
I know for a fact that the BNO carb is off a L/C chaparral in the early 70's . Not one of the greatest carbs to be using on a CAT.. Especially because most of the BNO carbs where used in pairs for the L/C chappy's. I would find a walboro or keihin for the cat. Much more reliable carb and correct for the cat...
What is the problem with the cat?
 

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If it`s off a Chaparral, it can only be off a 1974 model which all used BNO Mikuni carbs. Mostly all 42mm. The Thunderbird 440 use a single BNO 42 so this carb is capable of working well ,if set up right, on a Kawasaki 440 engine.
 

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Discussion Starter #6
I bought the 1974 Cheetah with a Xenoah 493 engine, which had "Chapparal" on the pull start recoil cover. last year my son filled the tank up and forgot the oil. Fried the engine. I didn't like it anyway because the engine didn't allow enough room for the headlight and the wiring was really screwed up. I purchased a kawasaki 440 off ebay. It didn't come with a carb so I used the one off the Xenoah.

The 440 runs great, and now I have room for a headlight, the wiring fits. I just think it just needs the carb tweeked so it starts easier and the throttle isn't so touchy.

I still have one carb adjustment screw I am not sure what it does? It is inside the carb, just in front of the butterfly. It has a knurled post and a notch so it appears that it was intended to be adjusted with fingers or a small screw driver.

I just installed new points and condensers too. Could incorrect timing cause this touchy throttle response?
 

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the carbs ARE off a 74 chaparral. i have had the same recent problems with my sled and nobody could help. so i went and got two round slide carbs that work fine for my chappy. trust me those butterfly carbs are JUNK!! ur carbs- mikuni bno42 carbs are very very nasty if you have them set n synched perfectly! but that is not easy so goodluck my friend. after i put my roundslide carbs on it made one heck of a difference. not quite as much power but plenty and wayyyy better on gas. trust me i know. ill sell you both my carbs if u want em for parts lol:cheeky4:
 

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Discussion Starter #8
Thanks for the info 74Chappy, I will take your suggestion and scrap the BNO for a slide. Snowmobiling season is almost over so finding and installing a new carb can be a summer project.
 
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