CR125 Low Compression

I recently purchased a running '04 Honda CR125 at the right price. The bike can easily bump start, almost too easily but it's a bear to get it to kick start. I'm getting 30 PSI on compression test and understand that's extremely low. Where do I need to start looking as I bought the bike with the top and bottom "recently rebuilt." But we all know recent is relative. Could the powervalve be the issue? No smoke and it's spitting a little, just need to dial the carb in. 

 

Also, anyone done the Keihin PWK Airstriker carb conversion for this bike?

 

The gears aren't shifting as smoothly as I would like and the clutch isn't smooth either. Where do I need to start looking for a hopeful easy fix?

 

I recently graduated from college and got back into bikes from when I was a kid, seems I almost enjoy working on them as much as riding. Thanks to @adnohguy's advice I ordered a service manual for the bike. That is a huge help but sometimes TT can't be beat. Thanks for any advice offered. 

 

 

first off, congrats on getting another bike.

 

how are you doing the compression test?  wide open throttle, kill switch pushed and about 10 good kicks?

 

and you are correct to assume that sellers are full of it when they claim fresh rebuilt.

 

the power valve will have little to no effect on starting.

 

I would get the low compression sorted out before changing the carb, more or less tossing money away if the one you have is set properly.

So a bike will not run with compression that low, check your compression tester and make sure it is working properly and also that you were doing it the way excitable said.

If you're getting me a reading of 30psi it's time for some teardown, my 125 regularly reads ~153-4; quite the difference

And like other have said triple check your comp tester

I had to have been doing the compression test incorrectly (no kill switch, no open throttle; this is slightly encouraging. Unfortunately can't get back to the bike til Friday night. Took yesterday off work and worked on it on my birthday. Thanks for the carb advice, no reason to throw money at it til I get it cranked via kick.

 

The air filter was disgusting so maybe just replace rings and see where that gets me? 

Yeah without having it at full throttle you will definitely get very low results as there is no air coming into the cylinder for it to compress. Kill switch doesn't change the results of the test but it removes the possibility of frying your ignition system from kicking it over and over without being grounded out.

Definitely replace the air filter and look at the reeds, they are probably chipped/broken.  That will make it hard to start.  Air filter/carb/reeds are a good place to start once you get a correct compression reading

Thanks for the explanation on compression, makes sense now with full throttle and on the grounding... 

 

Ordered some Vforce3 reeds and they will be in this weekend. Glad to know that should help with this issue as I was planning on putting them in anyway. 

 

Carb is the other thing I'm worried about right now. It won't idle worth a &*^$, hoping new jets will fix that. Is that where I should start? Haven't ordered them yet as I'm really interested in the Keihin PWK Airstriker conversion but like @excitable said there is no reason to throw money at it until I get the compression right. 

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