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Discussion Starter #1
I have a Piranha 125 motor bored out to a 131 with a big valve head thats ported and polished. i have a 26mm chinese mikuni with a oval-bore lever-choke. the bottom end to mid range isn't bad and runs good, but the top end sputters and chokes. I cannot get the jetting on this thing! Right now im running a 25 pilot jet and a 130 main jet. when i go up to a 135 main jet it just runs worse. any advice on jetting? is it the crappy china carb? i could use some help
 

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It sounds like you need a smaller main jet try going down a size and if it gets better keep goin down till it runs clean.
 

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Minibikaa said:
I have a Piranha 125 motor bored out to a 131 with a big valve head thats ported and polished. i have a 26mm chinese mikuni with a oval-bore lever-choke. the bottom end to mid range isn't bad and runs good, but the top end sputters and chokes. I cannot get the jetting on this thing! Right now im running a 25 pilot jet and a 130 main jet. when i go up to a 135 main jet it just runs worse. any advice on jetting? is it the crappy china carb? i could use some help


This is the site we use for a jetting guide



www.scootrs.com



Left side you will see



Parts

Scooters

Other - open this link, choose Tech - then #3a tune Keihin/mikuni carbs



Hope this helps,

Good luck
 

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yea dude, way to high on main, you need around a main between 110 and 117 max



those 26 mikunis that have the oval bore are more like a 24. was the 130 the stock mainjet?
 

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Mine did the same thing. Then I went to a main jet about 15, maybe 20 sizes smaller. No joke. Ran fine.
 

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Discussion Starter #9
thanks for all the help. from what everyones telling me and what those sites say; it seems like my main jet is too big. i'm gonna try main jets from 125-110 tomorrow and see how that works out.
 

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Minibikaa said:
its a 26mm. but it did come with that exact jetting
as a starter: A 26mm carb is too big for that engine if the head isn´t ported:rolleyes:

You will never get it dialed correctly, but as all said before , try a much smaller mainjet;)
 

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Try a #17.5 pilot jet and a #100 or #105 main jet with the jet needle in the 3rd or 4th notch from the top of the needle. Set the fuel screw at 1-3/4 turns OUT from seated, as a baseline to work from.



PM Member OLDSCHOOL did a nice write up on jetting a few years ago, addressing the Mikuni-clone carb you probably have.
 

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Discussion Starter #14
i messed around with it yesturday and i ended up with a 25 pilot and a 110 main and left the needle in the same spot. it ran like a whole new bike! now i just need a little more fine tuning and it will run perfect
 
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