● Click here to download the MSX/GROM 164 Ultimate Owners Manual.


● With its proven powerfull and reliable 160cc kit as its predecessor the all-new 164cc Ultimate kit is with the 1mm larger piston even a greater value for money kit where the Yuminashi R&D is not only introducing a slightly larger piston, but also a lighter piston with a molybdenum coating on the skirt to have less friction. (New piston not shown on the picture)

With the new Ultimate 164 kit you will have just like its predecessor a kit with improved performance/reliability and you can select a 12,000RPM limited Racing mode or a 10,500RPM limited Touring map which is really pleasant and perfect for touring with a lot more power as stock with still a surprising fuel economy.

Changing the map/mode is very easy. Once you have your stock ECU unit removed and our new stand alone ECU unit installed, you can select the Racing mode with installing the jumper that comes with the kit. With the jumper removed you go in to the touring mode where the RPM's will be cut at 10,500RPM's and this will allowe you to make a very safe top speed of 130Km/h or 80,78Mph with no risk at all on engine damage.

In the Racing mode you can drive as extreme as you want with a very safe state of mind because the Yuminashi R&D have covered this as well with programming the ignition timing and fuel injection amount in the standalone ECU based on the engines temperature.


If your engine temperature runs really high and your engine needs a break, then the ECU is programmed in such a way to give your engine a break with reducing the pre-ignition and adjusting the fuel injection amount to keep you away from piston and serious engine damage.

With all of this we can state very easy that the new Ultimate 164 kit is the safest kit for MSX/GROM125 on the market concerning durability and reliability where all parts where blue printed to be used with 91 and 95 octane pump gas (Europe) or 87 and 91 octane (Regular & Premium in the USA / Canada) and in combination with the stock throttle body and air filter (If you use the stock air filter you need to remove the restriction inside the stock air filter).

Your top speed in the Touring mode (RPM limited mode) will be 130Km/h (80mph), top speed in the non limited RPM mode will depend on the weather/road conditions and your personal body weight/hight.

The 10-holes MSX/GROM big bore injector that comes with the kit guarantee a short and powerfull injection and you don't need to install a larger throttle body or EFI controller to control the air fuel ratio because the standalone is programable (need to order the optional USB Programmer Cable)...

Set comes complete with the Yuminashi SX290  8.2 high lift camshaft, and also with the special high lift valves and retainers to make a higher lift as stock possible. 
The reinforced clutch springs that comes with the kit make sure that you don't miss one single RPM.

The piston from this 164cc Touring Kit is plug and play to be installed with the stock 125cc head.

This piston rings are produced on strict Japanes standards and since March 2015 are all rings treated with a hard chromium plating layer (Cr).

To read all details/information about the piston rings you can click on this link from the Yuminashi Direct Sales website...


 The MSX/GROM 164 TOURING KIT includes:


  • New Stand Alone PGMA-FI Programable ECU unit with overheating control to replace the stock ECU unit
  • Big Bore 10-Hole Fuel Injector
  • New design SX290 8.2 high-lift camshaft
  • Special High-Lift Valves set (25,5/21mm) for STD 125cc head
  • Progressive 2-Valve Spring set 14751-K26-000
  • 2 Special High-Lift Retainers
  • 4 Special Valve Cotters for the High-Lift Retainers
  • Reinforced Clutch Spring set (6Pcs/set)
  • Spark Plug NGK CR9E
  • 164cc Cylinder (60mm bore)
  • 164cc Piston (60mm)
  • 164cc Piston Ring Set (60mm)
  • 164cc Gasket Set (Head gasket & Cylinder gasket)
  • 13mm Piston Pin
  • 2 Piston Clips (13mm)


PRODUCT CODE: 12103-K26-590AU

PRICE: 17.182THB (388€ / 535USD) Exclusive V.A.T.

YUMINASHI DIRECT SALES   (Please check in the link section if there is a official dealer nearby before you click and use this service...)


WORD OF WARNING!! If you order and install a 150cc or 160cc for your MSX/GROM without a ECU mapped by our company, then keep in mind that you need to check the AFR ratio and people who have a fuel injection controller with the possibility to adjust the pre-ignition must be aware that to much pre-ignition will blow a hole in your piston.

We don't take responsibility if you get carried away with the amount of pre-ignition, and the damage that occurred because of it.

We recommend to install the PLX DM-6 SM-AFR wideband combo (click here to see the details).

If you don't install a wide band AFR gauge, and start playing around with a fuel injection controller without knowing where you are or what you are doing concerning the AFR ratio, then this will end up with an overheated/detonated engine where you will see a piston that is scuffed at the "four corners".

If you look at the bottom side of a piston you see the piston pin boss. If you look across each pin boss it's solid aluminum with no flexibility. It expands directly into the cylinder wall. However, the skirt of a piston is relatively flexible. If it gets hot, it can deflect. The crown of the piston is actually slightly smaller in diameter on purpose so it doesn't contact the cylinder walls. So if the piston soaks up a lot of heat, because of detonation for instance, the piston expands and drives the piston structure into the cylinder wall causing it to scuff in four places directly across each boss. It's another dead give-a-way sign of detonation. Many times detonation damage is just limited to this.

What typically happens is that when detonation occurs the piston expands excessively, scurfs in the bore along those four spots and wipes material into the ring grooves. The rings seize so that they can't conform to the cylinder walls. Engine compression is lost and the engine either stops running, or you start getting blow-by past the rings where you see your swing arm and rear wheel/tyre covered all over with oil. That torches out an area. Then the engine quits.

So install a wide band AFR meter en make sure that you are using an AFR ratio between 11.8 and 12.6 at high load, it's no problem to have 14.7 at iddle

!!If you installed a kit with only a cylinder and a piston, then be aware of the fact that if you order this kit you take your own responsibility for the well functioning of the kit. Our company will take no action if something went wrong with your kit.

If you have no exprience at all with tuning and mapping fuel injection bikes, then we stronly recommend you to order the 160 Ultimate kit. If you installed the Ultimate Kit and you have abnormal wear, then you can contact us at