Topic: Honda 1975 CB125s - Possible Carburetor Problem

[chriscraft42]

There are two issues I am having with my bike which I think has to do with the carburetor.

1. When bike is idling at about 1500 rpm it will stall within 1 minute.
2. When traveling over 40 MPH for a distance it seems to not get enough gas for the carburetor. If I am traveling around the neighborhood (short distances) the bike seems to run well.

Any suggestions - could it be the float?

Thanks...

[Chester345]

Hi, and welcome!

Need a little more info...all stock setup on your bike?  Have you tuned anything recently?

[chriscraft42]

replaced with a OEM carburetor this spring..never had the bike tuned since it only has 2500 miles and runs and starts well most of the time...

[Laminar]

What does your fuel line look like? Do you have an inline filter? How recently has your petcock been cleaned/rebuilt?

[Chester345]

On a bike that old, even with so few miles, going thru all the tuning motions might not be a bad idea.

Neat little bikes, I read that a slightly not full battery will cause all kinds of woes.  They can't charge up a battery much, just keep it up high when charged full.

I agree with Laminar's approach though, make sure you have clean constant fuel delivery from tank to cyl first...

[chriscraft42]

thanks for all the advice - I changed the petcock last year since the old one was broken. I may bring it to a bike shop to get a tuneup...

[mattcb350f]

1. When bike is idling at about 1500 rpm it will stall within 1 minute.
2. When traveling over 40 MPH for a distance it seems to not get enough gas for the carburetor. If I am traveling around the neighborhood (short distances) the bike seems to run well.
Thanks...

1....I've seen this on my own singles before when they stall while left to idle after a while. As the engine warms up, the required mixture changes and they stall. Try leaning out the idle screw mixture (the one just ahead of the bowl on the bottom of the carb). HOWEVER, if it stalls while you are on the throttle trying to keep it running it may be a bigger issue.

2.....If it's fuel starvation then check to make sure the cap is venting and the fuel is flowing out the petcock well. There may also be a problem inside the carb like float level etc.

You should also check the valve clearance.....I've seen too tight a valve clearance do the same things you seem to be having.


 Matt.

[1974blaze]

all of these things are true.  i have a 78 125s.  i went through similar issues.  after many carb adjustments, which led to little (though very lean mixture is best for me) i did a full tune.  set the points, twice, it helped a lot. but the valves was the last thing, and she runs smooth.  hang in there.