Carb Jetting Keihin List #071WBC For Bet & Win 250

[kymcomandan]

I was just wondering if anyone knows how the jetting is set up in this carb? I read somewhere that the jets only dictate full throttle response. Is that true? I felt surging at mid throttle the last time I rode my scoot & when I took it apart found gunk in the smaller jet that sits up above the floor of the carburetor bowl. There are two jets in this carb: One jet is lower in the bowl & the other sits a little higher up in the fuel level inside the bowl. My question is could the surging have been a result of the gunk in the second jet that I cleaned out or is cruise-to-mid throttle metering done without the jets?

[old geezer]

A basic outline of which jet is active at a particular throttle setting:
Pilot Jet = 0 to 1/4 throttle. Needle = 1/4 to 3/4 throttle. Main Jet = 3/4 to Full Throttle.
● Changing the Main Jet size won’t affect how your engine idles or runs at 1/4 throttle.

[kymcomandan]

Okay, so do you have any idea why it might be surging at mid throttle? Could the needle be moving even though the throttle is holding still? It does have a vacuum diaphram that controls the needle movement. Also I was wondering if there are any other fuel passages inside the carb that may be blocked or partially blocked that could cause the surging? This scoot only has 1200 miles on it so it doesn't have much wear & tear but it did sit for while. Tha gas in it now is good for sure. Idle runs perfect & so does wide open throttle.