Carby Tuning advice for Keihin carb

noah9988

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Jul 3, 2021
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So I got my engine running, and I've been messing with the carb tuning a bit. I believe I have a Keihin clone (see here). The bike seemed sluggish, so all I did was put the clip on the need up one (5 notches, from the middle one to one from the top). That helped. After this adjustment, I played with the idle mix and idle speed screws. The bike idles the highest when the mix screw is all the way in. Does this mean I need a bigger or smaller pilot jet? Or something else?
 

noah9988

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Jul 3, 2021
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Well now I feel like a dumbass for asking... I checked the spark plug, which I didn't before because I've ran it in different engines and didn't think I'd be able to tell anything. The plug was black and wet, so obviously it's running rich... what also should have clued me in is that I can start it cold without choke... I moved the needle up again to the top and the bike is running better. However, the air screw still needs to be turned all the way in.... do I need to change the pilot jet?
 

Karl Snarl

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remember you read the plug at the rpm you are checking. It will read different from idle to WOT if your carb is out of whack. May say rich on the bottom and lean on the top. You have multiple fuel circuits to tune on that carb. Start with the idle ( pilot) circuit, and move up from there. Then go back and readjust the idle when you dial in the top.
 

noah9988

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Will do. Although the only jets I can find are in a kit, with the smallest ones being a 70 main and 30 pilot. I don't know what mine are now because they are unmarked. It's $30 and I don't want to spend the money if it's not right.

Also the carb came with a tube that attaches onto the bottom of the float bowl, but as far as I can tell it doesn't do anything. There is also a small port on the side, do you know what is does?
 

Karl Snarl

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The one on the bottom is over flow. Can you take a pic of the other? Try a motorcycle shop for the jets, cheaper usually and you can get whatever ones you want in singles.
 

noah9988

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Can't take a pic right now. I don't think there are any places where I can buy them near me. Is there a way I can measure the size? I don't have micro bits or anything.
 

Karl Snarl

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Feeler gauge set

might be called a wire feeler gauge set. It's just a bunch of wires on a handle tht are set sizes. Jets aren't all measured by hole size, so be careful. Some are measured by flow rate.
 

Karl Snarl

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I'd first figure out what style you had. I know my 82' Kaw main and secondary are 5mm and measured by hole size, like with NT carbs. The pilot is a weirdo flute jet. It's what yours appear to be, but Idk for 100%, thats why I said be careful. But with a wire feeler gauge, you just lightly, so as not to damage the jet, poke the wires in the hole till it resists. You found the hole measured size by looking at what wire came before it.
 

noah9988

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Jul 3, 2021
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Alright, got some pictures. First one is just of the carb, second and third is of the tube and what it connects to. Forth is that port on the side, and fifth is underneath it, to show a small hole in it.
 

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