Cr125 low end lag/power, problem solving.

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1/1/2018 5:00 PM
Edited Date/Time: 1/1/2018 6:14 PM

Ok, i have a cr125 with a serious lack of low end power ( I know i know)... But it is an actual problem, and i can only liken it, too say turbo lag on a 2ltr car with a gt35 size turbo... I.E, nothing..nothing..nothing..Nothing..then power..
I'm looking for suggestions on what could cause this, and a guide to testing any parts/electricals in the hope of ruling things out as opossed to just stabbing wildly at the problem by buying new parts..

I do not think the problem is anything to do with the top end or carb, as i had two 03 cr125's at the same time and swapped the complete top end over and carb off the other bike, and it was still totally dead off the bottom, whereas the other one straight ripped.... unfortunately i sold the other bike so am unable to swap anything else over for testing/ruling out...

The back story on the engine in question is, it was dead off the bottom when i got it, it had rod knock and a 5mm chunk out the reed petals, knakered cylinder and piston.... so it's been fully rebuilt, crank/rod/bearings/reedblock/top end, plug etc.... and it still feels the same in terms of lag/lack of power low down as it did when it was knocking and had a 5mm chunk missing out the reeds....
Now i had a shop with a good rep build the bottom end, but i'm not ruling that out as a potential issue, if anyone could see why it could cause my symtoms.. maybe air leal, cracked casing, poorly fitted seal etc ?

Anyway, i'm thinking it could be anything off this list, if anyone has any other ideas, or some tips on how to test the electrical stuff, i.e what resistance etc i should be seeing, that would be greatly appreciated...

I'm thinking it could be any of this tbh, but i'm a noob so if i'm way off, say...

Kill switch,
Cdi box,
Powervalve govner,
Plug cap,
Leak in the bottom end ?

Thanks for reading if you got this far, i tried to give as much info as possible in the shortest way , but it's still a 'read'... but any help appreciated, i can see it getting expensive if the problems on the electrical side, as pretty much all the oem honda stuff is discontinued, and unfortunately i don't have an oem honda manual to get the resistance values to check the stuff i have sad

EDIT, bikes a 2003 cr125 incase anyone has a manual


1/1/2018 5:24 PM

Even most aftermarket manuals have those stats.

Paw Paw


1/1/2018 6:12 PM

Ok, i only have a 99-02 aftermarket manual, i was hoping someone may have the info i needed. But on a side note, do you think the parts i listed at the bottom could be related to my issue ?

I don't seem to have any problems on power when it gets there, and any ignition problems ive had with cars have been sort of opposite to this, i.e when under high/heavy load causing problems up top... am i looking in the right area with the electrics, or can my issues only be caused by a powevalve governor or air leak or something ?


1/1/2018 8:15 PM

Can you post a pic of the powervalve arm and linkage?


1/1/2018 10:24 PM
Edited Date/Time: 1/1/2018 10:31 PM


1/2/2018 3:20 AM

godog wrote:

Can you post a pic of the powervalve arm and linkage?

Yep, i will get one next time i'm near the bike, may be a few days though, but i feel it's not incorrectly set up as i've had the barrel off a few times, and it was as flat running the 134 it came on as it is the brand new 139 top end now, and when i put the 134 on the other bike it absolutely flew off the bottom... I've had the barrel off, and subsequently had to re set the powervalve tension so many times thst i'd like to think it's not that... but, it's well worth a second check so i will get a pic up, thanks.


1/2/2018 3:31 AM

Thanks mate, that top link looks ideal, but it's not loading up off my device so i'll hsve to wait to check until i can get to the laptop.

Had a quick read of the second link, i've done most the mods already and it's the same, which makes me think it's an underlying issue somewhere..... I think i may just buy a new powervalve governor, i don't want to buy used and get a potentially duff part, the only way to rule it out 100% is buy brand new.... Just a shame i sold the good cr before realising these issues were still here as i could've got the culprit nailed down in a morning with a good bike here for parts.

Thanks for taking the time to find those links for me though, much appreciated mate


1/2/2018 4:11 AM

In the pdf service manual you will find enuff to check everything.. If the problem is solved let us know what it was.

"too say turbo lag on a 2ltr car with a gt35 size turbo... I.E, nothing..nothing..nothing..Nothing..then power.."
Had the same with my cr250 BUT that problem was the basegasket. (1.2mm) now it's 0.6mm. That did change a lot to the bottom. Next step will be the original gasket to see how it runs and what it does to the bottom.