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92 CR125 low compression problem, need HELP!

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I'm having problems with my 92 CR125.

I've had the bike a few months now and it's been running great (within first month of having it transmission messed up, tore it apart, fixed trans and put all new bearings in entire bottom end, crank assembly felt good so re used it), not really too surprising because the previous owner obviously neglected the poor thing. Anyways, after the rebuild (all new bearings and seals along with a few new transmission components) the bike ran GREAT, TONS of power up top along with smooth power down low (125 so not neck snapping but it was properly smooth till it starts revving hard). 

Recently I started getting a bog down low when opening throttle quickly and diagnosed the cause being low compression (90 psi no matter how many kicks I give it, builds quickly to 90 but won't go higher, with throttle open/carb removed also. So I assumed it needed a new top end (same top end when I got it), so I put the wiseco kit in and unfortunately same psi readings, 90 psi, needless to say stuff went flying in the garage. Checked everything the manual said it could be like head/gasket, base gasket, reeds (replaced with brand new reeds), still 90 psi. Re-inspected cylinder bore and piston and they look flawless. I don't understand what else it could be, please help!

 

Im still currently riding the bike every weekend with the low compression, runs amazing well but I can feel the low compression when doing slow wheelies, bike dies out. It doesn't sound like it has an air leak, idles perfect and fires right up too, we ride for hours straight on the weekends and it never even flinches, runs excellent besides the low end bog (due to low compression), thanks for any help guys.

My manual did mention one last thing that could cause low compression and that's the crank seals, didn't know this could affect compression but the Honda CR125 factory manual says it can so I'm not sure what to do about that. Inspected left side crank seal (flywheel), zero wetness, I installed new crank seals 29 hours ago ( that's how many hours the engine has on it since I tore it apart). 

 

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Hmmm...I'm going to key in on what you mentioned...that the cylinder looks flawless. Did you measure or have the bore measured for wear? Still hone marks in it? Ring end gap checked? Mine just got torn down after reading 95 psi and the ring end gap was close to .070. Service limit is .026 so rings were severely worn. Piston measured and compared to the bore? Most local machine shops that do cylinder work will measure stuff....usually for free or a minimal charge at best. May be worth looking into so you know exactly where you're at....

 

And I'm still a little confused on the 29 hour mark....since bottom end work or since complete motor work including top end? I got lost a little there and not sure if you just replaced the top end and it has minimal hours on it and still reading low?

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29 hours since bottom end work, only have about 3 hours on the brand new top end (still low compression though).

Cylinder wasn't micd but it was inspected by me and it still has the cross hatching, didn't measure ring gap but I have a feeling its not dealing with rings because the compression was 90 before and after brand new top end, didn't change one bit. Cylinder had no grooving/obvious wear/damage at all when I checked, old piston was perfect, new piston is too. 

Considering that the compression was 90 before and 90 after the new top end, no change at all, makes me thing it's something else. 

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Hey guys, I'm back after all this time, I've been running the bike early every weekend since this post started and the bikes been running GREAT, does need a little jetting help but that's easy to do, either way, I found the problem. Turns out the compression tester wasn't sealing properly (sorry lol), i retested the bikes compression today just out of curiosity, 150psi, no problem, so for anyone out there like me that has run out of solutions, you never know, it could just be the tester (even though it worked perfectly on a yz125). 

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