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kx 125 bogging out

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Hi guys I bought a kx 125 that wouldn't start, figured out it was because the main bearings were shot and scored barrel, all fixed now. New main bearings, new piston kit and fresh gasket kit. 

 

It takes FOREVER to start (10min+) and when it does start it is super boggy all through the range, if you rev the hell out of it and get to really high rpms (almost hitting the power band) it will run pretty nicely but anything below that and it bogs. If I let it sit at low revs ticking over and then try to throttle it will bog so badly it will cut out, you have to rev it loads of times and build up.

 

The only thing "wrong" I can think of is I used an 03 piston in an 02 model bike because they didn't do 53.98 piston size for an 02 bike, the 03 piston has an extra port I believe but the store I purchased it from said it should run OK and I've asked the opinion of a few others who seem to think it should be ok to use.

 

The bike tends to run a lot better with choke on if that helps.

Also fuel comes out of the overflow on the carb when the bike is being kicked over.

Edited by Munch1

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The bike tends to run a lot better with choke on if that helps.

Also fuel comes out of the overflow on the carb when the bike is being kicked over.

 

The bike tends to run a lot better with choke on if that helps.

 --that would indicate the pilot jet circuit is perhaps blocked

 

Also fuel comes out of the overflow on the carb when the bike is being kicked over.

--the float level is too high, or the inlet needle not sealing / float not 'floating' properly

Edited by mlatour

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Check the compression, verify the ignition timing is set to the center mark on the stator plate and report back.  If the choke makes a difference it could be a carb problem.

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Check the compression, verify the ignition timing is set to the center mark on the stator plate and report back.  If the choke makes a difference it could be a carb problem.

 

Compression is perfect, ignition timing is a bit tricky to set up as I am using a 250 stator because my 125 died and the only one I could find locally was a 125. The notches on the 250 stator were obviously different to the 125 so I got the 125 plate and lined it up with the 250 stator and matched it all up so surely it should be ok?

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I would look real closely at that stator.  If it runs its close but if you're ten degrees off from optimal it'll run horribly.  If you're five degrees off it'll just run badly.  If you're within two or three degrees of optimal timing it'll run okay.  Only way to figure it out is to screw around with it.  Try advancing the timing slightly and see if it improves.

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