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Discussion Starter · #1 ·
The good folks over at Yumanashi have had the beautiful idea of grinding a bit of that pesky cylinder wall out to provide the bore of the stock 125cc motor to be inflated to a hefty 150cc's. The beauty of this is that the original throttle body will still be able to provide the engine with enough fuel and air to breath life into the inflated cylinder.


Work this in conjunction with their Light Bore Pistons, the kit needs only their Light Bore High Performance Injector kit. This kit utilizes the factory heads, valves, and even the ECU.


If you want, the kit allows for expansion beyond the 150cc range. You can bore this sucker out from 150, 160, 170, and even 180cc's if your little heard desires. All you would have to do is order the appropriate piston from Yuminashi, plug it in, drop one of their SX30 Heads on there and you are ripping down the pits with little to no abandon!
They have kits all the way up to 200cc's available for purchase. These include everything you need to get your little racer to scream past every other guy on a Grom. All of this can be bolted onto your bike for as little as ~$271.00 to $307.00…depending on the strength of the Thai Baht.


The MSX/GROM 150CC LIGHT BORE KIT includes:

  • 1 x 57.25mm Aluminum cylinder
  • 1 x 57.25mm Light Bore Piston
  • 1 x 57.25mm Piston ring set
  • 1 x Piston pin (13mm)
  • 2 x Piston clip
  • 1 x 57.25mm special Copper Head gasket
  • 1 x Cylinder base gasket

The MSX/GROM 160CC BIG BORE KIT includes:

  • 1 x 59.25mm Aluminum cylinder
  • 1 x 59.25mm Light Bore Piston
  • 1 x 59.25mm Piston ring set
  • 1 x Piston pin (13mm)
  • 2 x Piston clip
  • 1 x 59.25mm special Copper Head gasket
  • 1 x Cylinder base gasket

The MSX/GROM 180CC BIG BORE KIT includes:

  • 1 x 63mm Aluminum cylinder
  • 1 x 63mm Light Bore Piston
  • 1 x 63mm Piston ring set
  • 1 x Piston pin (13mm)
  • 2 x Piston clip
  • 1 x 63mm special Copper Head gasket
  • 1 x Cylinder base gasket

The MSX/GROM 200CC BIG BORE KIT includes:

  • 1 x 66mm Aluminum cylinder (Non painted aluminum to improve the cooling capacity)
  • 1 x 66mm Light Bore Piston
  • 1 x 66mm Piston ring set
  • 1 x Piston pin (13mm)
  • 2 x Piston clip
  • 1 x 66mm special Copper Head gasket
  • 1 x Cylinder base gasket

.::: YUMINASHI GLOBAL OFFICIAL WEBSITE - .::: MSX125 / Honda GROM CYLINDER KITS //

Thanks to CiscoSanJose for the tip: http://www.hondagrom.net/forums/7-grom-talk/466-big-bore-kits-grom-up-200cc.html
 

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To the point and makes it easy to see what you get. Thanks
 

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and they should list the optional parts right on the page. like add 150 injector 67, or add throttle body xx..... imo a complete kit would include everything. jus saying.
 

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upto 180cc for the big bore, anything more then its the sx30 head to go with, over 200cc then ya getting into new beefier engine cases etc, tells ya on the website or speak to reggy bodden, the guy who builds them!
 

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upto 180cc for the big bore, anything more then its the sx30 head to go with, over 200cc then ya getting into new beefier engine cases etc, tells ya on the website or speak to reggy bodden, the guy who builds them!
so we have to email them directly? i don't remember seeing any add to cart button or anything like that.
 

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nope ya get it from one of there authorised dealers but reggy bodden is the guy who builds them, there quality kit made from really good quality metal from Germany, no cheap crap, but I have had a lengthy convo recently with him as he is on my facebook friends, he aint in it for the money or mass production, just wants to make nice stuff at good prices, has no interest competing with t-bolt and any other engine gurus, I asked him to make videos etc but he hasn't the time but so many conflicting things keep me holding back, I must see someones bike who has had the tuning and parts fitted, I been quoted figures but I need to see with my own eyes, 150 bore kit with cam and injectors is making 80mph in the right conditions, I had 71mph on my standard msx the other day in very calm weather just after its first service which equates to around 66mph real world, if I was a 100lb thai riding it, I think these speeds are possible, I have seen msx vids of figures of 130kph so its possible but as to the mods they did I do not know!
 

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I'm not super excited about buying anything from over seas vendors. I think if I wait just a little while there will be plenty of companies here in the US selling the parts I want to purchase.
 

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I just want a 150 piston kit (no jug) and the "drop in" injector

Also guys keep in mind, I won't be able to confirm until I see a Grom/MSX throttle body but if it is the same as the PCX, you'll be able to upgrade to a PCX tb for cheap, brand new they're sub $120 and are 30mm

how you gonna run the bigger piston without the jug? gonna find the sleeve and bore your old jug? doesn;t quite seem worth the savings (if any) or do ya have tricks up ye sleeves?
 

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ps any speed figures for a 180 with head and injector and some sort of fuel tuning/cdi/higher rev limit?
 
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