carb tuning

jasonh

New Member
Jun 23, 2008
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You only have a couple adjustments you can make really: the idle speed screw and the needle for the main jet.

If you take apart the slide there is a long needle. This has a clip on the end of it. Stock position should be 2nd from the top. leave it there at first. Once you get the bike running you can set your idle speed to whatever you want it at. Ride the bike a few miles then shut down the motor and let it cool. Pull your spark plug and look at the tip. It should be a darkish tan color, maybe even the color of milk chocolate. If it's black and oily, you're running rich, if it's light colored or white, you're running lean.

If you're running rich, pull out the needle and move the clip up one notch. if you're running lean, move the clip down one notch. Clean the plug and test again.
 

CalgarysFool

New Member
Aug 30, 2008
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Jason,

Thanks for this crystal clear explanation. I'd read, several times of reference to this needle and the clip thing, but had no idea where it was, how to access it. I assumed my carb didn't have this, when I didn't see two adjustment screws on the carb body, like I'm used to seeing on older dirtbike carbs.

I think I'm running rich, even with a 24:1 fuel/oil mix.

Very helpful.

Cheers,

Brenton
 

CalgarysFool

New Member
Aug 30, 2008
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Wait a sec. I'm confused again. The screw for the main jet...

Is this attached to the choke?

As I mentioned, I see only one screw -- the one that adjusts the idle up and down.

: /
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
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63
up north now
There is no screw for the main jet. You adjust the clip by removing the slide and taking the needle out of the slide, moving the clip up or down, and re-installing the needle/slide top of the carb.

You can also fine tune these engines by other methods, such as tapering the jet needle (you can get a slightly richer setting at any needle setting this way), opening up the air filter cover with some holes (makes it leaner, but you have to make a lot of holes) drilling or cutting part of the baffle inside the muffler (makes it leaner) and adjusting your gas/oil mixture. (more oil will make the overall mix leaner, less, richer- but don't even think about this if you are not really adept with small 2 cycle engines)

Best to stick with the needle clip adjustments for the newb.
 

lilhog

New Member
Dec 25, 2008
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florida
I turned the screw too many times and dont know how to get it back to stock. Many carbs turn in all the way and then out a certain amount of times. Does anyone know?
 

CalgarysFool

New Member
Aug 30, 2008
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I think it is 2 and 1/4 full rotations to stock position.

Hey Joe, ... About this "slide" --- ahh, where is it? How do I find/access it?

TIA, as in "Thanks in advance" or, "transient iscemic attack", i.e., this bike might just cause me to have a stroke.

;-)

Thanks,

Brenton
 

CalgarysFool

New Member
Aug 30, 2008
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Ah-Haaaaaa! There it is, bottom of page 2 -- it's under the screw-off toppy thing into which the throttle cable goes!

Phewww!

Thanks,

Brenton
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
236
63
up north now
I turned the screw too many times and dont know how to get it back to stock. Many carbs turn in all the way and then out a certain amount of times. Does anyone know?
Yes, turn the screw out 2 turns and see where it idles, adjust from there. They all seem to be different. The idle screw just moves the slide up when screwed in, so there is no magic number of turns.
 

jude

New Member
Feb 16, 2009
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australia,nsw
how do u tune these things?
Gunson Colortune , this is a glass sparkplug that you can see threw , going by the colour of the explosion inside the combustion chamber these are the best engine tuning devise for Lean & Rich Mixture Adjusting , check them out on EBAY , GUNSON COLORTUNE & YOUTUBE.
 

CutterSpaulding

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Dec 9, 2019
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I got one for a 26 inch bike...mine is 24inch....so cables are a lil long. I fixed the clutch cable(easy). But the throttle I'm having problem with how would remove the slack of cable cover? Without nodding the steel cable itself? Any thought be appreciated. Thanks