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Author Topic: CB125S Engine HELP  (Read 1201 times)

Offline trek97

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Re: CB125S Engine HELP
« Reply #30 on: Apr 06, 2017, 22:37:54 »
Im fresh out of ideas.  Seems youve double checked everything.

 >:( frustrating.

Build her back to stock and see if she is still running as good as she originally did.





Offline natez

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Re: CB125S Engine HELP
« Reply #31 on: Apr 06, 2017, 22:43:39 »
ugh! Kinda over it :( wish I didn't touch it in the first place.

Offline trek97

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Re: CB125S Engine HELP
« Reply #32 on: Apr 07, 2017, 05:05:07 »
No, they wont run properly without a battery.   :o  Thats the reason they include a battery from the factory. 

What type of battery do you have?

Im not familiar w the Radio Shack rectifier.  Is is a solid state unit?  Regulator/rectifier?

Offline natez

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Re: CB125S Engine HELP
« Reply #33 on: Apr 07, 2017, 15:06:16 »
Don't remember the part number off hand, but it's a brand new yausa. Same bat it had in it before I took the motor apart and it ran fine. I even unhooked all the lights and ran it with a 12v battery yesterday (google search cb125 12v conversion, totally kosher to do), starts and idles way better, but unfortunately still loses power past half throttle.

Lots of old threads on the net about the radio shack rectifier. Not sure on its specifics but I did it years ago. I think its only a rectifier. Think I am going to toss the motor and stick a 200CC Lifan in the bike so atleast the whole thing isn't a total loss. Total pain in the ass to rip the motor all apart again just to see if it runs correctly stock, got too much other stuff goin on.

Offline natez

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Re: CB125S Engine HELP
« Reply #34 on: Apr 07, 2017, 15:14:47 »
Can I rule out incorrect setting of the timing chain/sprocket/cam? If the cam was incorrectly set  by one tooth on the sprocket/chain would it run so well at idle and up to half throttle?

Offline teazer

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Re: CB125S Engine HELP
« Reply #35 on: Apr 07, 2017, 15:16:59 »
Just ran it with the timing light. The static pointer is dead on the T mark at idle. When you rev it up timing advances to the left hand of the two timing marks. It strobe doesn't miss or anything when you start to rev through the bogs so I guess we can rule out an ignition issue.... That damn carb is clean as a whistle, float is set right. I haven't tried it with no main jet yet, but when you move up in jets from 100 (100 is what another person with the same motor and carb went with after he did the same cylinder conversion) to 125, the miss/bog remains the same however it begins to smoke a bit more. Pull the plug and its darker/sootier.

At idle, the timing should fire at the F mark.  Try to advance the ignition timing until it does.  Then the advanced timing should be closer as well.  That should improve things.

Offline furu14

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Re: CB125S Engine HELP
« Reply #36 on: Apr 08, 2017, 03:14:09 »
What about air filter? my XL600 stops dead in its tracks at 5000rpm WOT with those popular steelmesh-podfilters.replaced them w longer runners with foamfilter on end-7500rpm clean..

Try removing the airfilter/snorkel.