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Discussion Starter #1 (Edited)
I've got a 1975 CB125 winter project in rough condition that I'm trying to bring back. I got it to start up but the engine cuts out when I give it a little throttle. Any suggestions? I installed a new filter (when it turned out there was no actual foam filter in the air box) and cleaned the carb jets. The spark plug is still the original one. Any suggestions are appreciated.
 

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Cleaning the carb requires thorough cleaning of the entire body, especially the small passages that route the fuel from the jets to the venturi. The jets themselves are seldom the problem. Submerging the carb in traditional solvents or in an ultrasonic cleaner are effective alternatives.

You'll need a gasket set available at CMSNL, possibly others, Honda part # 16010 107 305.
 

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I've got a SL125 that was running tits, and suddenly it started doing the very same thing...and kept right on doing it even after I cleaned the carb three times! Did you ever figure it out?
 

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How much rust comes out of the tank? The small jets in your carb. are very sensitive to small particles of rust,etc. from in the tank.
Did you adjust your valves yet or clean/inspect your points ?
 

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I did all that before it started acting up, it was TITS and had been gone through completely. Plus the tank isn't rusty, the coil showed no signs of going bad and after cleaning that carburetor in the ultrasonic at least three times, I just put it in the shed. But since I found a fairly complete parts bike, I'll take your word for it and take the other carb, clean it and see what happens. My buddy had one of them as his first bike, rode it across the USA, and him and me both had everything dialed in and tuned to where that thing was just great, until this bull**** rained on my parade: Starts and idles great, but falls on its face the instant you open it up. So thanks for that, I'll check it out.
 

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Discussion Starter #7
Kind of an old thread, but I started wrenching on my 125 last week and seemed to sort out the problem. I don't know exactly what did it, but I did do the following: recleaned the carb, including blowing out the ports with an air compressor, replaced the spark plug, replaced the fuel line and in-line fuel filter, refilled the tank with a new tank full of gas.
 
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