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Discussion Starter · #1 ·
I decided to sell my non-running ex250. I had originally thought it was just the carb messed up. Guy came to look at it yesterday and did a compression test on it. Both cylinders read about 90. He then added a bit of oil and it jumped up to about 180.

I have never compression tested before, so I can't say if it was done correctly or not, but I had thought that you were supposed to have the airbox on it and the throttle wide open to get an accurate reading. The airbox was disconnected from it, and the throttle was closed when he did the test.

Anyway, if it's confirmed that the compression is low, is it worth it to invest in replacing the pistons/rings, or is it better to just part out the bike? I really don't want to put any more money or time into fixing it, but with the compression being low is there anybody that would find value in buying the motor as it is and fixing it up themselves?
 

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I don't know if it matters if the airbox is on or not, but I do know the throttle needs to be wide open. The oil is to see if it is valves or rings. In your case it would be rings if the test had been done with the throttle open.
 
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Discussion Starter · #3 ·
I don't know if it matters if the airbox is on or not, but I do know the throttle needs to be wide open. The oil is to see if it is valves or rings. In your case it would be rings if the test had been done with the throttle open.
With the throttle closed, would that cause there to be low compression? I don't have a compression tester, but if there's a chance the readings were wrong because the throttle wasn't open, I can borrow one or go buy an inexpensive one to re-test myself.

If it ends up being that the rings are bad, do you think it's worth it to pull the motor and replace the rings?
 

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You probably wont notice a difference with it open or closed. The proper way is with it open cause its more accurate. It has to do with air. The main thing is being consistent. Do all cylinders the same way, not one with throttle open and the other closed.
Only you can decide if its worth repairing
 

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Sometimes it can make a difference whether the throttle is open or closed so personally I would try to test again. Check your local auto parts store - a lot of them have loaner tools. Hey, if you're local to NH by chance you can borrow one of mine.

If you do confirm the rings are spent it's probably not financially worth it to do the rebuild - you will likely not recover the parts cost. Parting out the bike or just selling it as-is would probably be the best thing. Some folks do buy project bikes.

But, confirm the compression test before jumping into that. What year is the bike?
 

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it would cause a lower reading for sure. Only you can decide if it is worth spending the money to rebuild it.

(though I had sent this yesterday)
 

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Well I guess it depends on the bike because I just did a compression test on my son's cbr last summer and didn't open it at first. Then I remembered and tried again and didn't notice a difference
 
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