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1975 Honda CB125S running rich above 5000 rpm

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Trying to get my wifey's bike running again after a 30 year hiatus.

I've cleaned the tank,fresh fuel filter.soaked and cleaned the carb installing new needle,seat and float,new points set to .014,trimmed the plug wire back 1/2" and verified timing,removed old foam from air filter and cleaned the mesh screen it locates on.

The bike starts and is rideable but above 5000 rpms it starts to bog and cut out. I've tried the choke at this point but it only makes it worse.It acts like it is running too rich but I'm not sure how this could be.The exhaust pipe is in good condition and does not seem to be plugged up bot not sure how to verify that.I am going to check compression and valves next but not convinced that is the problem.

Would a bad condenser or coil cause this? I'm not sure how to test those. Also it does get worse as the bike warms which makes sense if it is running rich to begin with.

Any help is appreciated!

 

Blakeslee

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  I would suspect that the needle jet and jet needle are worn .

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Well, I replaced the condenser and there was no change. I should have listened to nsman :prof: ......I pulled the intake off the back of the carb and while revving the bike noticed whole fuel droplets coming out of the needle jet area. At idle the fuel atomization looks good and the bike runs clean.

Soooo I'm on board with the needle and jet replacement unless there is something else I should check first.

I'm having a tough time finding carb parts for this model. Who has these parts available other than ebay?

I'm going to try my local dealer first but don't want to get scalped.

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Ebay had a Napco kit for $31.00 delivered that included a new needle jet etc. I'll let you know if that does the trick once installed.

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The kit arrived and after installing new needle jet and needle it still stumbled. Put the old needle in with the new needle jet and she's almost perfect!

The new needle had a completely different taper than the old.....not sure why. Have a slight off idle lean bog so going to raise the needle a bit and see if that solves it. As it is right now she is at 95%. Thank you for the help.....much appreciated!

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