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2001 cr 125 won't start

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I just rebuilt the top end on my bike I replaced the cylinder jug and piston along with all the gaskets I went to start the bike it starts right up for about 2 seconds and dies out put a new plug fresh gas swapped out ignition coil and carb can't get this bike to run at all I checked the compression and has 120 psi anyone know what else to look for????

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Depending how you did your compression test, 120psi is extremely low.

A freshly rebuilt & broken-in 125 should get at least 160+ psi.

 

Is the piston directional in that model CR?

(is it 'windowed' on the intake side skirt?)

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If it fired up (got spark and compression) but quits, 

it kinda leaves fuel delivery as the culprit.

 

Have you tried firing it up with the first ignition coil again?

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Depending how you did your compression test, 120psi is extremely low.

A freshly rebuilt & broken-in 125 should get at least 160+ psi.

 

Is the piston directional in that model CR?

(is it 'windowed' on the intake side skirt?)

Compression seems very low. Did you do it at WOT ?  Are you sure you installed a right size piston ? Since they come in 0,01 mm increments. The other thing is the squish band. Have you measured it and if so , how much was it? Was the plug wet when you took it out ?

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Yes it is directional I used a wiseco piston stock bore size

thts the problem a wiesco piston should be in a ported jug and have a little shaved off the piston to a roundshape 

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thts the problem a wiesco piston should be in a ported jug and have a little shaved off the piston to a roundshape

There's no need for any kind of porting because of wiseco piston. You just need to be sure you have the correct size and make sure your squish is ok. Set your squish at 1mm.

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I have now got the bike running I found the piston ring was upside down but I can only keep it running at a soft idle holding the gas lightly or else it shuts off on me

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Check the jetting and compare it to what pro circuit has on their support page. Or if you have the Honda manual compare what it says. Did you measure the compression with wide open throttle ? Did you measure the squish band ? On our - 02 Cr the squish was way too big. It was 1,3mm and now we're running with 0,85mm. That transformed the whole bike and now it actually works

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