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Yz125. Feels like its gonna seize.

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We completely rebuilt our yz125 this last month, new top end bottom end, bored out. We broke it in and took it to the track today for some fun but it did some things that have left me scratching my head:confused:

I took it out for a few laps and about 3 times the thing would just stall in a corner like it was starting to seize up. It kinda scared me but it keep running and idled fine:excuseme: . The 3rd time it stopped and I could not kick it over. I though oh $hit I blew it:foul: W-T-F I put it into neutral and pushed it off the track. I then kicked it over with a good couple of kicks and it fired up and idled:confused: So I gave it back to my lil bro and he rode it the rest of the day with no problems.

What in the world was it doing and what would make it do that?

I'm seriously confused, help:crazy:

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i've had old suzuki 125's seize up on me, then once it cooled down it simply re start and keep running, all be it poorly, opened it up afterwards and it was a very minor lean seizer, not enough to drop the compression enough to kill it, but enough to warrant a new piston and a re bore (this wasn't a plated bore, an old iron sleeve), pull it down and see what the barrel's like, if you had just started the engine it could be a case of cold seizing it as well.

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i've had old suzuki 125's seize up on me, then once it cooled down it simply re start and keep running, all be it poorly, opened it up afterwards and it was a very minor lean seizer, not enough to drop the compression enough to kill it, but enough to warrant a new piston and a re bore (this wasn't a plated bore, an old iron sleeve), pull it down and see what the barrel's like, if you had just started the engine it could be a case of cold seizing it as well.

It has a sleeved cylinder and I made sure the bike was warmed up before I rode it. I asked my bro how it was running after and he said it ran perfect:confused:

I would feel a lot better knowing it had a plated jug instead.

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pull it apart and see what it look's like, if all looks well then look at the kick starter, could have been binding or had something stuck in the gears which would be why you couldn't kick it.

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you should have seen if you could push start it after you tried kicking it, that would have told you pretty much the whole story.

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How big did you bore it out and what ratio and jetting where you running. In my experiances big bores like extra oil. The CR125R my riding buddy has with the Wiseco 139 kit on it refuses to run lower than 32:1. He siezed on 40:1 even with their jetting recommendations.

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How big did you bore it out and what ratio and jetting where you running. In my experiances big bores like extra oil. The CR125R my riding buddy has with the Wiseco 139 kit on it refuses to run lower than 32:1. He siezed on 40:1 even with their jetting recommendations.

this man speaks the truth.

a bigger bore is gonna have different requirements than before :thumbsup:

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How big did you bore it out and what ratio and jetting where you running. In my experiances big bores like extra oil. The CR125R my riding buddy has with the Wiseco 139 kit on it refuses to run lower than 32:1. He siezed on 40:1 even with their jetting recommendations.

It was just bored out to accept the next sized piston wiseco makes. I think it would make it a 128cc? I would just expect it to seize completely after what it did with me on it but no:confused:

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if the bike has not been re-jetted for the new mods your running to lean thus starving the top end of oil.

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Did you measure the ring gap before you installed the piston? Did you measure the piston to cylinder clearance? Pull the exhaust off and have a look at the exhaust side of the piston... make sure there is no scoring.

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