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Why only 110 psi.

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Rebuilt the top end on my sons 03' CR125 two weeks ago Complete OEM top end gaskets and everything . With a new OEM cylinder from Honda. Started it up and was super boggy so i figured it was jetted wrong since the old top end had over 40 hrs. and the pretty drastic weather change . I never really messed with it until today got the carb issues all straightened out and runs great. I figured i would check compression , write it down and use it for comparison later after he got some time on it . I checked it with a brand new Craftsman compression tester and could only get it to 110 psi. Throttle wide open , reeds look good ( newer Vforce ) Just has me stumped any ideas ?

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What's the normal PSI range for a fresh 125 motor?? Sounds not too bad..

I'm not sure for this model but was called wrong today on here when i said 125 psi. wasn't bad on a 125cc . It runs strong but still a moped after riding the 250 for awhile  :lol:

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Sounds low to me. I checked the compression in my yz125 and it showed 185 psi. Yes my user name is deceiving

Edited by THE.CRF.RIDER
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I'm not sure for this model but was called wrong today on here when i said 125 psi. wasn't bad on a 125cc . It runs strong but still a moped after riding the 250 for awhile :lol:

I'm pretty sure a "healthy" 125 top end should be 150 to 180 or so. With all new oem parts I would think there is an issue with 110 psi. How does it run? Does it start good? Does it have any power?

The CR's of that vintage were known to have very weak engines, 110psi won't help that....I would check to see if the PV is stuck? The electronic RC valves are always suspect, or potentially an air leak? With all the new parts it should be something simple, good luck.

Edited by poldies4

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And why are you up at 230 am? I can't sleep. Sux.

I couldn't sleep either. So I stayed up and did a week worth of homework lol. Edited by THE.CRF.RIDER

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I'm pretty sure a "healthy" 125 top end should be 150 to 180 or so. With all new oem parts I would think there is an issue with 110 psi. How does it run? Does it start good? Does it have any power?

The CR's of that vintage were known to have very weak engines, 110psi won't help that....I would check to see if the PV is stuck? The electronic RC valves are always suspect, or potentially an air leak? With all the new parts it should be something simple, good luck.

It runs awesome just like it should, it has governed power valves not electronic , i pull the pipe and PVs every few weeks to clean and oil but did check , worked them manually . Has all new gaskets even rebuilt the waterpump at that time and replaced all the seals , bearings . Replaced the engine side cover , clutch cover, and PV gaskets . It didn't leak down after getting to the 110psi. Cause i left it on there looking at it in disbelief.  :facepalm:

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Did u mic the cylinder. And u mentioned u used a craftsman gauge. I'd borrow one from someone to double check it. And did u kick it over a few times

Edited by Jdrost72

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It runs awesome just like it should, it has governed power valves not electronic , i pull the pipe and PVs every few weeks to clean and oil but did check , worked them manually . Has all new gaskets even rebuilt the waterpump at that time and replaced all the seals , bearings . Replaced the engine side cover , clutch cover, and PV gaskets . It didn't leak down after getting to the 110psi. Cause i left it on there looking at it in disbelief.  :facepalm:

 

A compression tester won't tell you if you have a leak in the crankcase.  You have to build a leak tester and pressurize the crankcase and then see if you lose pressure over a time period. 

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It runs awesome just like it should, it has governed power valves not electronic , i pull the pipe and PVs every few weeks to clean and oil but did check , worked them manually . Has all new gaskets even rebuilt the waterpump at that time and replaced all the seals , bearings . Replaced the engine side cover , clutch cover, and PV gaskets . It didn't leak down after getting to the 110psi. Cause i left it on there looking at it in disbelief.  :facepalm:

Sorry for your luck. Like Blackwoodz said, I'd check out the tester and verify that it's accurate. I guess since it's running good it could be that? Good to know the 03 has a governed PV, thanks for the info.

Maybe the wrong size piston? A piston with a B cylinder sort of thing?

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Sorry for your luck. Like Blackwoodz said, I'd check out the tester and verify that it's accurate. I guess since it's running good it could be that? Good to know the 03 has a governed PV, thanks for the info.

Maybe the wrong size piston? A piston with a B cylinder sort of thing?

Yea, Honda doesn't categorize like that anymore i called after ordering the nikasil cylinder and they said they are all A cylinders . With it all being new i only checked ring gap , and cylinder wall clearance with a feeler gauge. I don't have a bore gauge . I'll pressurize the cases and see how that goes , I guess  just let him rip it for another 40-50 hours and do it again. :)  

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