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I was looking today at what big bore parts there are for the Grom. This seems to be closest to what I can get and would need to ship from USA since I'm in vancouver. .::: YUMINASHI GLOBAL OFFICIAL WEBSITE - .::: MSX125 / Honda GROM PGM-FI Tuning

"These High Performance Fuel Injectors are looking exactly the same at first sight as your genuine MSX125/GROM injector, but have 2 extra holes that you need if you start to work with the larger, +150cc displacement Big-Bore cylinder kits."

I think this is what I'd need, and looks to be $70. Is there any who have done MSX 125 update like this and maybe instruction on how so I can see if I can do in my friends garage? sammy
 

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I did some research and these injectors are meant to be paired up with the Yuminashi bore kits.

They have injectors meant for the 150cc kit, and the 150cc+ kits.


This Light Bore High Performance Fuel Injector looks exactly the same as your genuine MSX125 fuel injector, and you only can see, or better said, feel, the difference once you have installed it on your MSX125 in combination with the Yuminashi 145cc Light Bore Piston set (to bore your genuine 125cc cylinder up to 145cc), or with the full 150cc light bore cylinder kit.
This injector is not mentioned to be installed in the 31mm throttle body, but very simply to replace your genuine 125cc injector in your genuine 125cc manifold.
Like this you don't need to buy any electronic device for your PGM-FI to upgrade your stock 125cc until a light bore 145cc or 150cc.
**The Light Bore High Performance Fuel Injector is not recommended to be used in a full stock 125cc MSX125 engine...



This High Performance Fuel Injector is mentioned to be used on the Big Bore kits in combination with the big valve heads.
These High Performance Fuel Injectors are looking exactly the same at first sight as your genuine MSX125/GROM injector, but have 2 extra holes that you need if you start to work with the larger, +150cc displacement Big-Bore cylinder kits.
These injectors don't fit in our 3-sensor PGM-FI 31mm throttle body, but can perfectly be used in combination with our 34mm PGM-FI 3-sensor throttle body.
**This injector would fit in your genuine MSX125, but is overkill on an engine less as 160cc...
If you start to work with the Big-Bore or Super-Bore cylinder kits, then keep in mind that you need to check, and control the AFR ratio (Air Fuel Ratio) from your engine, not only to improve the performance, but also to keep your engine alive.
We recommend an AFR ratio from 13.2:1 (this means the stoichiometric Air–Fuel Ratio (mixture) where for every gram of fuel, 13.2 grams of air are required).
The Air Fuel Ratio inside your engine is changing all the time, and we know from experience that in a high performance engine with a high-lift/ longer duration cam like the Yuminashi SX270 camshaft, a peak at high engine load of 14:1 is allowed.
Anything higher as 14:1 at high engine load will increase the risk on detonation/pre-ignition dramatically, where you blow a hole in your piston as soon as you hit the 15:1.
To avoid this, you need to install our High Performance fuel injector on the big bore and super bore kits, and you need to check then your AFR ratio to see where you are.
If your AFR ratio is to high, which means a to lean stoichiometric air-fuel mixture, then you will need an electronic device to correct it.
**Make sure that you are checking your AFR ratio with a wide band O2 sensor. The narrow band sensor like the MSX125/GROM and all motorcycles have installed standard is useless to measure the accurate AFR ratio.


They also sell a 31mm throttle body set

This 3-Sensor YUMINASHI 31mm PGM-FI Throttle Body (MAP sensor (Manifold Absolute Pressure Sensor), IAT Sensor (Air Intake Sensor), TP Sensor (Throttle Position Sensor) with EACV (Idle Air Control Valve)), is mentioned to bring your simplified 1-sensor genuine MSX125 / GROM PGM-FI system without an Idle Air Control Valve and only a TP Sensor to a higher level and ready to be used to get the best optimal performance/potential out of your engine.
This set comes complete with all sensors installed, inclusing the High Performance Fuel Injector and the Idle Air Control valve, plug & play ready to be programmed (if you have a programable ECU unit) to achieve the best possible results...

This throttle body has to be used with a special wire harness, and 3-sensor racing ECU and the YUMINASHI 31mm PGM-FI Manifold Set for Honda MSX125 / Honda GROM.
The venturi is machined in to a stack to optimise and achieve an improved velocity. The entire inside of the throttle body is mirror shine polished.
**For racing applications best performance will be achieved without air filter. For road use we recommend original air filter K&N R-1100.
 

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I guess it would be nice to have more power in the GROM but is it really that slow? I mean isn't that the whole point of the GROM? To be low power and user friendly?
 

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Wow I don't believe I've never clicked on the tabs on the left. I'm such an idiot.

Check this out..

SUPER BORE CRANKCASE SET (186CC UNTIL 217CC)



The maximum displacement possible for MSX125 with the original crankshaft and genuine Honda crankcase is 180cc.

The Yuminashi R&D has developed a 150cc Light Bore kit to use with the original Cylinderhead and valves for MSX125, and a 160cc and 180cc Big Bore kit to install on the original, genuine Honda crankcases and crankshaft with the Yuminashi SX30 HEAD (30/24.5mm valves).

If you want more, then you will need these Yuminashi Super Bore crankcases who are prepared to accept the Yuminashi 210cc (68mm piston) Super Bore Cylinderkit to install on the original stroke MSX125 crankshaft.

The Yuminashi Super Bore Crankcases are not painted black as original, but unpainted aluminium and this for the simple reason to improve the cooling capacity from the engine.

The Yuminashi SPR-X HEAD for the 210cc Super Bore cylinder kit with 33/26.2mm valves is based on our racing experience with the Yuminashi SP200R factory engine.



The Super Bore Crankcases set for MSX125 includes:

1 x Left Crankcase
1 x Right Crankcase
1 x Crankcase Gasket Yuminashi
2 x Pin, Crankcase




YUMINASHI SX30 HEAD (150cc UNTIL 175CC)
The Yuminashi SX30 Head is specally developed to be used on engines with an displacement from 150cc (57,25mm) until 175cc (62mm).

The YUMINASHI SX30 HEAD has reinforced valve guides and special anti-magnetic stainless steel valves with titanium retainers and a 30mm intake valve with 24,5mm exhaust valve to be used with the eye on competition purposes.

The anti-magnetic stainless steel intake valve has a 4,5mm stem and the diameter from the anti-magnetic stainless steel exhaust stem is 5mm.

The YUMINASHI SX30 HEAD comes complete with titanium alloy retainers and double progressive valve springs which are a perfect combination to make the highest RPM's possible, and an absolute improvement compared with the genuine single MSX125 / GROM valve springs with steel retainers.

The YUMINASHI SX30 HEAD includes:

1 x Aluminum non painted cylinderhead to improve the cooling capacity
1 x 4.5mm Titanium valve retainer
1 x 5mm Titanium valve retainer
1 x 30mm special stainless steel anti-magnetic intake valve
1 x 24.5mm special stainless steel anti-magnetic exhaust valve
2 x Double progressive valve springs, reinforced
1 x 4.5mm Cotter valve set
1 x 5mm Cotter valve set


YUMINASHI SPR-X HEAD (180cc UNTIL 223CC)

The Yuminashi SPR-X Head is developed with our racing experience from the Limited Edition Yuminashi SP200R Factory engine, and is mentioned to be used on MSX125 / GROM engines from 180cc (63mm) until 223cc (70mm).

The SPR-X Head has reinforced valve guides and special stainless steel anti-magnetic valves, with a 33mm intake valve and 26,2mm exhaust valve.

The intake and exhaust valve has a 5mm stem and the head comes complete with 5mm titanium alloy retainers (3Gr.) and double progressive valve springs which are an absolute improvement compared with the genuine single MSX125 / GROM valve springs with steel retainers.


The YUMINASHI SPR-X HEAD includes:

1 x Aluminum non painted cylinderhead to improve the cooling capacity
2 x 5mm Titanium valve retainer
1 x 30mm special stainless steel anti-magnetic intake valve
1 x 24.5mm special stainless steel anti-magnetic exhaust valve
2 x Double progressive valve springs, reinforced
2 x 4.5mm Cotter valve set


PROGRESSIVE DOUBLE VALVE SPRING CONVERSION SET

This double valve spring conversion set is mentioned to convert the genuine, single valve spring MSX125 / GROM head in to a head with double progressive valve springs to avoid the floating valves.

If you start to tune your engine up for higher RPM's as standard, then the first issue to be solved will be the problem from the floating valves on the MSX125 / GROM.

This set includes 2 steel retainers mentioned for the genuine 5mm valve stem, and if you would like to have the racing version from this set, which is also available with 2 titanium retainers, then please look below...

The color on the valve springs is mentioned to give you a help to install them correctly. Because these valve springs are progressive valve springs you need to install them with the colored side up.

RACING PROGRESSIVE DOUBLE VALVE SPRING CONVERSION SET

The Racing double valve spring conversion set is not only mentioned to convert the genuine, single valve spring MSX125 / GROM head in to a head with double progressive valve springs, but to relief the valve train and squeeze the full potential out of your cylinderhead.

If you start to tune your engine up for higher RPM's as standard, then the first issue to be solved will be the problem from the floating valves on the MSX125 / GROM.

This set includes 2 titanium retainers from 3Gr. each, mentioned for the genuine 5mm valve stem...

The color on the valve springs is mentioned to give you a help to install them correctly. Because these valve springs are progressive valve springs you need to install them with the colored side up.

TITANIUM ALLOY 5MM/5MM RETAINER SET

Titanium alloy retainer set.

If you start to tune your engine up for higher RPM's as original, then the first issue to be solved on the MSX125 / GROM will be the problem from the floating valves.

This set can be installed on the genuine MSX125 cylinderhead to make some higher RPM's with the genuine single valve spring possible. This set includes 2 x 5mm retainers. The weight of 1 retainer is 3Gr…


TITANIUM ALLOY 4.5MM / 4.5MM RETAINER SET

This set comes standard in the Yuminashi SX30 & SPR-X Head and can not be installed in the genuine 125cc cylinderhead.

Set includes 2 x 4,5mm retainers. The weight of 1 retainer is 3Gr…

● Titanium alloy retainer set for a combination of a 4.5 and 5mm valve stem. This set can not be installed on the genuine MSX125 cylinderhead and is a replacement part for the YUMINASHI SX30 HEAD.

This set includes 1 x 4.5 and 1 x 5mm titanium alloy retainers mentioned for a 4.5mm and 5mm valve stem. The weight of each retainer is 3Gr…

If you start to tune your engine up for higher RPM's as original, then the first issue to be solved on the MSX125 / GROM will be the problem from the floating valves.

This titanium alloy retainer set comes standard with the big valve YUMINASHI SX30 Head for MSX125 / GROM.

**YUMINASHI SX30 HEAD has one titanium alloy retainer 4.5mm, and one titanium alloy retainer with 5mm...
 

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Wow I don't believe I've never clicked on the tabs on the left. I'm such an idiot.

Check this out..

SUPER BORE CRANKCASE SET (186CC UNTIL 217CC)



The maximum displacement possible for MSX125 with the original crankshaft and genuine Honda crankcase is 180cc.

The Yuminashi R&D has developed a 150cc Light Bore kit to use with the original Cylinderhead and valves for MSX125, and a 160cc and 180cc Big Bore kit to install on the original, genuine Honda crankcases and crankshaft with the Yuminashi SX30 HEAD (30/24.5mm valves).

If you want more, then you will need these Yuminashi Super Bore crankcases who are prepared to accept the Yuminashi 210cc (68mm piston) Super Bore Cylinderkit to install on the original stroke MSX125 crankshaft.

The Yuminashi Super Bore Crankcases are not painted black as original, but unpainted aluminium and this for the simple reason to improve the cooling capacity from the engine.

The Yuminashi SPR-X HEAD for the 210cc Super Bore cylinder kit with 33/26.2mm valves is based on our racing experience with the Yuminashi SP200R factory engine.



The Super Bore Crankcases set for MSX125 includes:

1 x Left Crankcase
1 x Right Crankcase
1 x Crankcase Gasket Yuminashi
2 x Pin, Crankcase




YUMINASHI SX30 HEAD (150cc UNTIL 175CC)
The Yuminashi SX30 Head is specally developed to be used on engines with an displacement from 150cc (57,25mm) until 175cc (62mm).

The YUMINASHI SX30 HEAD has reinforced valve guides and special anti-magnetic stainless steel valves with titanium retainers and a 30mm intake valve with 24,5mm exhaust valve to be used with the eye on competition purposes.

The anti-magnetic stainless steel intake valve has a 4,5mm stem and the diameter from the anti-magnetic stainless steel exhaust stem is 5mm.

The YUMINASHI SX30 HEAD comes complete with titanium alloy retainers and double progressive valve springs which are a perfect combination to make the highest RPM's possible, and an absolute improvement compared with the genuine single MSX125 / GROM valve springs with steel retainers.

The YUMINASHI SX30 HEAD includes:

1 x Aluminum non painted cylinderhead to improve the cooling capacity
1 x 4.5mm Titanium valve retainer
1 x 5mm Titanium valve retainer
1 x 30mm special stainless steel anti-magnetic intake valve
1 x 24.5mm special stainless steel anti-magnetic exhaust valve
2 x Double progressive valve springs, reinforced
1 x 4.5mm Cotter valve set
1 x 5mm Cotter valve set


YUMINASHI SPR-X HEAD (180cc UNTIL 223CC)

The Yuminashi SPR-X Head is developed with our racing experience from the Limited Edition Yuminashi SP200R Factory engine, and is mentioned to be used on MSX125 / GROM engines from 180cc (63mm) until 223cc (70mm).

The SPR-X Head has reinforced valve guides and special stainless steel anti-magnetic valves, with a 33mm intake valve and 26,2mm exhaust valve.

The intake and exhaust valve has a 5mm stem and the head comes complete with 5mm titanium alloy retainers (3Gr.) and double progressive valve springs which are an absolute improvement compared with the genuine single MSX125 / GROM valve springs with steel retainers.


The YUMINASHI SPR-X HEAD includes:

1 x Aluminum non painted cylinderhead to improve the cooling capacity
2 x 5mm Titanium valve retainer
1 x 30mm special stainless steel anti-magnetic intake valve
1 x 24.5mm special stainless steel anti-magnetic exhaust valve
2 x Double progressive valve springs, reinforced
2 x 4.5mm Cotter valve set


PROGRESSIVE DOUBLE VALVE SPRING CONVERSION SET

This double valve spring conversion set is mentioned to convert the genuine, single valve spring MSX125 / GROM head in to a head with double progressive valve springs to avoid the floating valves.

If you start to tune your engine up for higher RPM's as standard, then the first issue to be solved will be the problem from the floating valves on the MSX125 / GROM.

This set includes 2 steel retainers mentioned for the genuine 5mm valve stem, and if you would like to have the racing version from this set, which is also available with 2 titanium retainers, then please look below...

The color on the valve springs is mentioned to give you a help to install them correctly. Because these valve springs are progressive valve springs you need to install them with the colored side up.

RACING PROGRESSIVE DOUBLE VALVE SPRING CONVERSION SET

The Racing double valve spring conversion set is not only mentioned to convert the genuine, single valve spring MSX125 / GROM head in to a head with double progressive valve springs, but to relief the valve train and squeeze the full potential out of your cylinderhead.

If you start to tune your engine up for higher RPM's as standard, then the first issue to be solved will be the problem from the floating valves on the MSX125 / GROM.

This set includes 2 titanium retainers from 3Gr. each, mentioned for the genuine 5mm valve stem...

The color on the valve springs is mentioned to give you a help to install them correctly. Because these valve springs are progressive valve springs you need to install them with the colored side up.

TITANIUM ALLOY 5MM/5MM RETAINER SET

Titanium alloy retainer set.

If you start to tune your engine up for higher RPM's as original, then the first issue to be solved on the MSX125 / GROM will be the problem from the floating valves.

This set can be installed on the genuine MSX125 cylinderhead to make some higher RPM's with the genuine single valve spring possible. This set includes 2 x 5mm retainers. The weight of 1 retainer is 3Gr…


TITANIUM ALLOY 4.5MM / 4.5MM RETAINER SET

This set comes standard in the Yuminashi SX30 & SPR-X Head and can not be installed in the genuine 125cc cylinderhead.

Set includes 2 x 4,5mm retainers. The weight of 1 retainer is 3Gr…

● Titanium alloy retainer set for a combination of a 4.5 and 5mm valve stem. This set can not be installed on the genuine MSX125 cylinderhead and is a replacement part for the YUMINASHI SX30 HEAD.

This set includes 1 x 4.5 and 1 x 5mm titanium alloy retainers mentioned for a 4.5mm and 5mm valve stem. The weight of each retainer is 3Gr…

If you start to tune your engine up for higher RPM's as original, then the first issue to be solved on the MSX125 / GROM will be the problem from the floating valves.

This titanium alloy retainer set comes standard with the big valve YUMINASHI SX30 Head for MSX125 / GROM.

**YUMINASHI SX30 HEAD has one titanium alloy retainer 4.5mm, and one titanium alloy retainer with 5mm...

210cc big bore kit WTF..... that's nearly 100cc more than stock. I guess with that big bore kit we could expect nearly double the power? would that be a good guesstimate? 18bhp n/a would be nice.
 

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If your AFR ratio is to high, which means a to lean stoichiometric air-fuel mixture, then you will need an electronic device to correct it.
This is the device we need. At the end of the day it's still best to be able to have a device to tune the fuel input.

I am going to assume the wideband o2 would just replace the narrow band? Should be universal.
 

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This is a little bit embarrassing but I have no idea what the valve springs and crankcase do.
 

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A lot of money there it looks like
 

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Without getting too technical the valve springs are needed to solve an issue called valve float where the valves just float and don't actuate the entire duration at high RPMS. You can imagine at very high RPMS (speeds beyond the capability of the stock valves) the stock springs are getting slammed on often and if they aren't designed to be rigid enough to snap back / extend you get what is called float.

The springs and retainers will toughen up the valves to handle higher RPM. The crankcase is only meant for those who are planning to bore out the engine beyond 200cc. The crankcase holds the crankshaft.

Do these bore kits come with the pistons?
 

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How much power are you gaining with all of this?

Say the super bore kit. Injectors, bore kit, crankcase, throttle body.
 

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Is anyone actually selling these kits? I can't find them for sale anywhere.

It's hard to say how much power. I don't have much experience with bore kits. The last time I owned anything below 600cc was 12 years ago.
 

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Is anyone actually selling these kits? I can't find them for sale anywhere.

It's hard to say how much power. I don't have much experience with bore kits. The last time I owned anything below 600cc was 12 years ago.
I think being this early in the stage of the kits being where they are at you'll have to go directly to the source and ask them about availability, price, etc. Doesn't seem like any vendors have these bore kits listed on their sites.

If there's enough of a demand I bet our Vendor, Tyga, will be all over it.
 

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Is anyone actually selling these kits? I can't find them for sale anywhere.

It's hard to say how much power. I don't have much experience with bore kits. The last time I owned anything below 600cc was 12 years ago.
found a website
Honda MSX , Grom 125,

a better photo of the kit as well
 

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of course it does! We haven't really figured out how exactly to do so yet :)
 

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Im waiting for the arrival of the grom in the US. but what I would really like to see is a drop-in Yuminashi complete motor available. and yea they are supposed to be eco-friendly but i can sacrifice 50mpg for some more fun lolol =P But what i genuinely like about this bike is the small frame, light weight, and cost friendly. as i do not plan on doing much freeway riding. i would like this to be able to hit 80, and not even because i wanna go 80, i just dont want to have this little motor screaming for help at 65mph.
 

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I am also curious how much performance gain you can achieve out of their 180cc kit. hp? rpms? torque? top speed? you can probably change the sprockets to get you to 80 i would imagine or gear them towards flying like a bat out of hell to 50.
 
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