CB125T Idle

[S1417]

I posted a while ago about my CB125Ts carb setup and was told that they probably just needed a cleaning, so I did that to no avail. The bikes fine apart from when its idling, it tends to hang around 4k but fluctuates randomly up to 5k and down to 2k, trying to reduce the idle speed just stalls the engine.

Then I got fed up with them and had a garage look at them, he couldn't solve the problem either. So I decided to try taking the carbs off of the spare bike and spent all afternoon cleaning them and then trying to set them up. The problem still wasn't fixed and it ran exactly the same

So what am I missing? Could something else be causing this?

[Commuter_Tim]

Firstly, the following is taking for granted that your mechanic was a numpty and/or didn't give a shit, its only a 125, why should they care?
Also making the assumption the CB125T uses mikuni carbs.

IME fluctuation of idle RPM can be an air leak alongside the carb (among other things).
When you're adjusting the idle speed screw, are you also adjusting the fuel mixture screw? (are you sure that isn't the only screw you're adjusting?)

How is your air filter looking?
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The above post is most likely nonsensical.

I ride a Bandit 600... badly.

[mattday]

Vacuum leak definitely sounds the most likely cause. What is the condition of rubber couplers between carbs and inlet stubs?

[Fizzer Thou]

I had exactly this same problem on my CB125T2.The 'O' rings between the cylinder head and the inlet manifolds had split in numerous places.Once replaced,I was able to set up the carbs using vacuum gauges and achieved a consistantly stable tickover
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Just talk bikes.What else is there?

Always have a 'Plan B'