stroker 139

I read alot on the big bore 125s on here but have not seen anything with a 56mm bore and a 56.5mm stroke.

Does anyone know if this combo would work well?

I'm sure it could be pretty good. If you're going the trouble though, why not go bigger?

I built a 144stroker and love it. 56mm bore, 58.5mm stroke

Any bigger and you would need a larger pipe to get the most out of the motor.

Any gearing or jetting suggestions?

13-48 is on it now.

The jetting is stock at 40 pilot 410 main.

My guess is that you could go 13-47, 14-50 or 14-51. I ran 13-48 on my bored 134 and had to short shift it.

Any bigger and you would need a larger pipe to get the most out of the motor.

OEM pipe seems to work really well with yz144. Mine does.

Any bigger and you would need a larger pipe to get the most out of the motor.

It depends on port timing mainly. If the porting is adjusted accordingly, an OEM pipe will do fine.

So far I am going with the GYTR pipe and 13-47 gearing to start.

I am leaning towards uping the main jet to a 430. My riding style is to run it like a chain saw, it should be a screamer.

...I am leaning towards uping the main jet to a 430...

Generally, with an increase in displacement, you'll need to go leaner on your jetting.

Your 139cc motor will now be pulling in more air & gas -- more gas than what is optimum. Your results may vary, as they say. But keep that in mind. :thumbsup:

I suggest changing the main jet only if it needs to be changed.

OEM pipe seems to work really well with yz144. Mine does.

Gorr advised using the stock pipe and and shorty silencer on my pump gas mo' betta '05 YZ144

Gorr advised using the stock pipe and and shorty silencer on my pump gas mo' betta '05 YZ144

I got the same suggestion from Harris Performance. It seemed to work well on my stroker 144, but it seems like it prefers a longer silencer.

From what I've read, shorter silencer helps low end, longer silencer improved over rev.

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