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Old 08-29-2011, 04:00 PM
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Default 89 CR125 help

Hi, my 1989 CR125 has recently started to run funny. It seems to be losing power at high rpm but not at low or mid range, at top rpm it starts to sputter but not all the time. The bike starts easy and runs great right up until the high revs.

At first I though the bike just needed a rebuild, but after finding that it still 125PSI at the top end, now i'm not so sure. I was thinking it could be electrical or it could the power valve (ATAC) stuck. Any ideas?

thanks
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Old 08-29-2011, 04:04 PM
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Quote:
Originally Posted by raf2325 View Post
Hi, my 1989 CR125 has recently started to run funny. It seems to be losing power at high rpm but not at low or mid range, at top rpm it starts to sputter but not all the time. The bike starts easy and runs great right up until the high revs.

At first I though the bike just needed a rebuild, but after finding that it still 125PSI at the top end, now i'm not so sure. I was thinking it could be electrical or it could the power valve (ATAC) stuck. Any ideas?

thanks
The ATAC units didn't really work very well, and if it was stuck open it would theoretically be where it worked better on the bottom end than the top. You should be able to pull the bottom of the unit and see if it is moving as you rev the motor.

Have you looked at your carb and the float to check the height?

Thanks
scott
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Old 08-29-2011, 04:49 PM
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Default Compression

Your compression is a bit low and thus you may be seeing blow by at high rpm. You should be at about 160psi compression. At 125 psi it should run, but not real good at top rpm and may seem to bew running rich.

Paw Paw
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Old 09-05-2011, 02:31 PM
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Hi everyone, I found out what the problem is. I had lost a special bolt that goes in the cylinder to stop the power valve from moving to far and opening the power valve a high RPM, It must have vibrated out.

But anyway I decided to rebuild the top end since i need the special bolt (which honda discontinued) for it to run proper anyway.

so I got her stripped down and the piston doesn't look to bad but the cylinder does. I noticed that i can still see the marks from when it was honed or whatever but only on the sides, not around the intake or exhaust ports. Is this normal? i'm guessing not.

Worst of all the cylinder bore seems to be out. I don't have an inside micrometer so i just placed the piston ring inside the cylinder and used the piston to push it down in 1/4 increments. Around have way down the cylinder the ring end gap opened up big time, I just eye-balled it.

What now? can i bore nikisil? or do i have to send it for re-sleeving?

thanks guys
`
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Old 09-05-2011, 03:37 PM
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look around, dont get it sleeved, get it bored and replate it. you can buy a piston a bit oversized and send it with the cylinder and they will bore it out and plate it to match that piston exactly. i did it with my rm250 i replated. thats your best bet, getting a cylinder sleeved isnt the best thing to do to a bike...
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