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Big bore

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Big bore

PostAuthor: Lawbreakingtrucker » Fri Aug 25, 2017 2:25 pm

I've read threads 6 and 7 years old threads about big bore for the 250 engines..
Do any of You guys still ride these bikes and did the engine modifications work for a longer period of time?
I've just got my first bike this year and I love to work on it in my garage. This winter I will give it some more power and I'm looking into making it a 280cc engine. If any of You guys that tried this in the past will point me in the right direction I would appreciate it a lot.

My plans for the bike is inspired by Larish41, bigger homemade exhaust (1-3/4"), 52mm pistons (280cc), maybe bigger carburetor and changing the sprockets to 17/40.

Any thoughts on this for my clonebike? Jinlun Spartan JL250V
retsis ti esool ro ti evoM

Lawbreakingtrucker
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Re: Big bore

PostAuthor: Lawbreakingtrucker » Fri Oct 13, 2017 11:40 am

Anybody who can help me with wich pistons that will fit the 2V49FMM engine. I wanna go up to 52mm but dont know wich other dimensions the piston needs.. and from wich other engine can I use the piston.
retsis ti esool ro ti evoM

Lawbreakingtrucker
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Re: Big bore

PostAuthor: eslmatt » Fri Oct 13, 2017 7:47 pm

Seems like you have some fabrication skills :bg: or are at least willing to learn.

I have an xv750, but also a Chinese 110 that I over-bored to 125 (with a kit)

This particular bike was not popular in China, so there is no aftermarket big bore kit. I checked. If they used a Jl110 piston. (Chinese copy of a Honda Super Cub) it will be easy to fit a larger piston 52mm. It may get a lot more complicated if not. The hardest thing is finding measurements on replacement pistons.

One of the most important measurements is the wrist pin to top of piston. This will alter your compression even a 1 or 2 mm off will make a big change.

So, when your riding season is done, pull the engine apart and get the piston out. Search for piston measurements on 125cc engines. If you are very lucky someone will have done this upgrade.

When you figure it out, post it here and have the mods mark it (solved) it will help the next person doing this.
1984 VX750 Japanese special - stolen - RECOVERED
build thread -> http://viragotechforum.com/viewtopic.php?f=32&t=58187&sid=e4ab82933609aa211c1efb06cf000508

2010 Jailing 110 customized

When asking how, also tell me why.

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