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There seems to be a number of people here with carburetor problems and a lack of information on the Keihin Carburetor. The Klymer manual basically tells you how to take them apart and put back together but not how to trouble shoot them.
Wondering about the function of the air cutoff valve .What is it's function? How do you test the air cutoff valve? There is only vague information available on these carbs. My Clymer manual talks about checking the cutoff valve on # 1 carb only. Why is there no information available on these carbs? Everybody seems to be just guessing. I spent hours on the internet looking for information and came up with nothing.
If someone here knows of a Manual that covers these carbs, the function of their sub-systems, trouble shooting etc would you please post it here.
Thanks, Karl
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I read your comments with much interest and have to agree with you entirely. Finding technical information about these carbs is like looking for a needle in a hay stack. My Australian workshop manual only shows the diaphragm, spring and O ring, but doesnt tell you what purpose it serves ,other than its an air cut off valve. I did read in the forum several weeks ago what the air cut off valve was for and how it worked, but where to find it - your guess is as good as mine. I cant find the post about the diaphragm anywhere, but will still keep trying , unless of course its been deleted. I might do a Google and do some research on the subject and if and when I find anything I`ll put a post in the forum about it. Cheers, Peter
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My 75 750 does not have an air cutoff valve but my Goldwing does. If I recall, it is to reduce fuel flow to eliminate backfiring and popping when you decelerate. I don't believe it has any effect on idle or throttle up circuits. The accelorator pump does. It provides smooth throttle during acceloration. If this is not working right, the engine will stumble. They are both rubber diaphrams with springs. I'm finding out in a hurry that the 750 carbs have to be dead on perfect to run right. I do work with a person who was a Honda mechanic back in the 70's so he has helped a lot. Mine was running like crap after I overhauled my carbs and he told me to drop the needle jets 2 notches. That was the trick!
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CB750Winger wrote
My 75 750 does not have an air cutoff valve but my Goldwing does. If I recall, it is to reduce fuel flow to eliminate backfiring and popping when you decelerate. I don't believe it has any effect on idle or throttle up circuits. The accelorator pump does. It provides smooth throttle during acceloration. If this is not working right, the engine will stumble. They are both rubber diaphrams with springs. I'm finding out in a hurry that the 750 carbs have to be dead on perfect to run right. I do work with a person who was a Honda mechanic back in the 70's so he has helped a lot. Mine was running like crap after I overhauled my carbs and he told me to drop the needle jets 2 notches. That was the trick!
Okay so how does one drop the needle jets? Can this be done on the carbs for a 1981?
Cat
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Sorry Cat, I know the 81 carbs are much different and I can't really tell by the Honda drawing if the needle jets are adjustable. Have you had yours apart yet? I still think they would come out through the top. Paul
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This post was updated on .
The DOHC Keihin CV's do not come with adjustable needles. The dyno jet jet kit comes with them, and pretty much a necessity for getting 'pod' air filters to work decent. Carbs work best with airbox, period. Great 'upgrade' for most climates is to richen the primary main jet from 68 to 75, regardless of pipe/etc.As far as truely undersanting these things...I don't. The constant velocity, vacuuum slide carbs are very different in function to any other carb I've dealt with. Well, similar in theory, but when it comes to applying that theory it never seems to work for me...LOL. In short I know how to make them work, and just ride them. For performance gains/modded motor/racing completely different carbs are recommended (accel pump, cable lift...ALA Keihin FCR), and these apply to what I know about carb theory in much more sensable fashion...LOL
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Unfortunately the carburetor covered in the link mentioned in the previous post is the old three barrel for the CVCC car. Not at all what we're playing with.
Karl
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Well, after three attempts I finally got the carburetors working, synchronized and all.
Had to separate the carbs from one another for soaking. Now I need to clean the tank. There is a light
coat of rust that wipes of easily. Now I need to figure out what to use to clean it with.
Maybe a strong detergent along with some media like a hand full of gravel, shake it up, rinse it.
Any ideas?
Karl
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One of my favorite home concoctions was heavy soda water, and then use alcohol to get the water out.
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Hello woodsrider250, would you please define "heavy soda water" and the procedure you used?
I am thinking of buying a product called EVAPO-RUST. Anyone ever hear of it or use it? It is quite costly.
Thanks,
Karl
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Meant water mixed heavily with baking soda. That product looks like it would work great.
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I am missing the small oring in mine. are they hard to come by?
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Locked
