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I recently bought my first bike, the lovely 75 Honda bc 125s. I LOVE it, and have been able to do most of the maintenance myself.

I’ve run into one continuing issue: about once a week she will decide she no longer wants to idle, and will die at stop signs. I’ll usually have to wait about ten minutes before kicking her on again.

I’ve replaced the oil filter, fuel filter, air filter. Her carb is new but I cleaned it again anyway and had the floats adjusted. Scrubbed down the gas tank for any debris and rust, adjusted the throttle, the idle speed and air/gas intake, switched to supreme fuel but no dice.

I heard from someone who used to own one back in the ‘80s that they had a similar issue until they started adding a fuel mixture...

Any idea if this could be the issue? What’s a good fuel additive to try?
 

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Motorbike Macgyver
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I’m fairly certain you mean cb, not bc. And if it takes ten minutes to start again, that could be a fouled plug, I’m guessing it’s either that or a bad ground getting hot somewhere. I’d check all your grounds first to make sure they’re, well, actually grounded and then I would check them all for continuity, if all that checks out I would pull your plugs. If they come out black and wet, they’re fouled.
 

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Chances are the valve clearances have never even been looked at.

You don't need fuel conditioner unless you have a fuel condition problem; for instance if you have water in the gas you add isopropyl alcohol and that combines with the H2O to make something that can pass through the engine.
A 1975 CB125 is like a little Honda generator, it will run on almost anything that resembles fuel.
 

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Hi, new member here, But I would have the compression tested when cold and hot, sounds like a classic "thermal expansion" of the piston rings. when cold they are probable ok, but with heat, all metals expand, and with age and wear, it may be getting too tight in the cylinder to allow it a free movement.
 
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