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 Product Description

free-shipping-worldwide-new-big-.png164 LIGHT BORE ULTRA POWER PACK (PCX125 LED / SMART KEY & 2018 DIGITAL GENERATION / 13MM PISTON PIN) 

● The 164 Light Bore ULTRA kit is the perfect kit for anyone looking for an amazing kit with the emphasis clearly on the power side…

This ULTRA kit has been developed to give you total control and to remove the stock RPM limiter entirely to make maximum performance possible. We recommend installing a wideband AFR meter to make AFR datalogging possible to get the perfect tune.

The name "Light Bore" is a reference to the fact that this entire kit has been developed to be used in combination with the stock 125cc cylinder head. 

The 164cc cylinder in the Light Bore ULTRA kit has been designed with the 125 water cooling holes pattern.

The design from the special 60mm light bore piston make a seamless install possible with the stock 125 cylinder head. (Keep in mind that a 150 cylinder head cannot be installed on this type of cylinder...).

All parts in this kit are very well balanced to be installed on your PCX125 LED, SMART KEY or DIGITAL and all parts in the Light bore ULTRA kit are easy to install. 
Normal motorcycle / scooter mechanical skills are required, and with the deeper valve pockets in the 60mm piston we recommend to set the valve clearance at 0.05mm intake valve / 0.08mm exhaust valve.

We recommend to modify the stock exhaust, or to install the Silent Sport exhaust from our Takegawa colleagues in combination with this kit to get the full power potential of the kit.




● Taking tuning to the next great leap with adding the YUMINASHI STANDALONE ECU in the 164cc ULTRA PACK for PCX125 LED/SMART KEY & 2018 DIGITAL.

At YUMINASHI, we understand that a fully standalone for the PCX engines are not technically possible because unlike other bikes, the Engine Control Module (ECM) for these engines contain also the starter function as well as battery recharge.

This problem has prevented the emergence of a stable, truly open source standalone ECU for the PCX engines for years.
However, we have solved this problem with a special wire loom in order to let you connect a true standalone ECU to your stock wire harness.
Please be noted that your stock ECM would still need to be installed in order to start the bike and recharge the battery. The rest, however, is fully controlled by you, the tuners through our standalone software.

Since this is a standalone ECU, the RPM limit will be removed, and you the tuners have full control over almost everything. Injection control, both the amount and the timing of the injection event as well as ignition timing, and enrichment circuits to compensate for cold engine start are all available to tuners who want to take advantage of them and allow for a much more precise tuning experience which will undoubtedly lead to a better running engine and higher performance.

You will need to buy a wideband O2 gauge as well as this optional data link cable (if you want to physically connect the ECU to your laptop or PC) or to bring your scooter to a dynamometer service which can perform air fuel ratio tuning in order to take the most advantage of this standalone ECU unit.

This Standalone ECU is Bluetooth enabled!
If you have an Android phone, you can use Bluetooth to tune the Air Fuel Ratio setting yourself!..

(Click on the image below to visit the Google Play Store page to install the API software for free on your Android phone) 


This means that your wide band O2 gauge can be connected to your standalone ECU and read wide band AFR data while you are driving on your Android system!!


This means also that you can see the AFR ratio in each and every field, and that you are able to adjust/correct these fields on the fly with your Bluetooth Android system!
This eliminate basically the need for a dyno since you are able to make all these correction while you are driving and this based on real life load conditions like uphill driving, or facing a headwind, etc... 


While the software can run with the stock Honda narrow band O2 sensor, it's absolutely useless to start tuning based on the stock narrow band O2 sensor.
We strongly suggest not to do so since it's a total waste of time and money if you are doing so.

The stock 1 volt narrow band sensor isn't able to read accurate AFR reading, so the results you will see on your screen will be far away from accurate/reality with possibly serious engine damage as result!...

If you don't have a wide band O2 gauge yet, then we like to recommend the Innovate MTX-L PLUS gauge (please click the link in yellow, this device is not supplied by our company).
This California based company has a basic no nonsense device which can take a lot of vibrations, it's perfectly visible with daylight and is it's just perfect to do the job compared to others we tried...


It's also very easy to connect this gauge to our standalone ECU.
You only need to connect the yellow wire from the MTX-L gauge to the green wire from our standalone ECU
, and after a right click on the AFR meter from the program you need to select "wideband".

Once you did this you can start your engine and see exactly next to each value in the map how much the AFR ratio is from any particular spot in the map and like this it becomes really easy to know if you have to increase or decrease the percentage from that particular value in the map to get your optimal AFR target.

The Air Fuel Ratio (AFR) below 75% TPS throttle can be 14.7 AFR for good fuel economy, we recommend with WOT (Wide Open Throttle) 12.3 AFR.

If you have set your perfect map, then keep in mind that your AFR ratio will change based on the temperature.
If it's starting to get colder or warmer compared to the temperature when you had set up your map.

If you don't have an Android phone, then you can download the tuning program below, open the the software on your computer (you need to use the USB tuner Cable for that, software is free), go to "enrichment correction" and enter a value based on the actual temperature to get your entire map back like it was when you had set up the map.

Like this you are able to correct and set up your standalone ECU to run your tune day in, day out.


 Click on this link to open the App page in the Google Play Store, where you can download the API app for free to connect your Android phone with bluetooth to your standalone ECU.

● Please open this PDF file and use it as a guide to gain both, maximum performance and maximum protection against engine knock (very important).

**Click this link to download the tuning program manual in PDF file...

             Driver install software (1.6M)



                  2017 ECM-BLUETOOTH V9.1 Tuner Setup software 2017 (1.97M)

**Click on this link to download the .msi file needed to install the tuning program.

● The Torque Control Variator Set is the cherry on the cake in the package which will improve both, acceleration and top speed. 

The 8 gram roller weights are included in the set.


● The 31mm throttle body is 25% larger compared to the stock PCX125 throttle body, and the reason why this much larger throttle body is included in the kit is because the stock throttle body is a serious restriction for the much larger amount of air sucked in by the 164cc big bore piston. Removing the stock throttle body and replacing it by the 31mm throttle body allows the engine to suck as much air in as possible, and opens the full potential of your engine in combination with the big bore kit.


The new Stainless Steel Bracket/throttle cable holder is installed on the new 2018 model 31mm throttle body.


● The special throttle cable 17910-KWN-910 for the 31mm throttle body comes with the set together with the 5-Pin Wire Loom to make the install a truly plug & play experience. 

17910-kwn-711.png 32101-k36-000-5-pin-connector-loom-pcx150-led-.png

 ● The 6-Holes B-Type High Flow NLJ-injector is included in the kit for the simple reason that sucking more air in the engine with a much larger piston and a 25% larger throttle body requires more fuel to keep the perfect balance between air and fuel. 
This is important of course for the performance of the engine, but also for the reliability since a lean running engine would have overheating issues. Selecting the right injector is really important and with including the right injector in the kit you can be ensured your engine gets the fuel it needs to get.

**With the standalone ECU you can adjust the fuel amount to get your Air Fuel Ratio based on your location, humidity and altitude really spot on. Barometric pressure is highest at sea level and decreases with altitude. A reduction in atmospheric pressure requires leaning the fuel mixture.  


 ● The 31mm B-Type Manifold Set is included in the kit to make the install from the injector and the throttle body a truly plug and play experience. The stock injector joint from the PCX125 can be installed on this manifold and injector to connect your fuel hose.


  ● The 1.6 High Pressure Cap which comes with the set is to make sure your cooling system can control the extra power and doesn't open premature at 0.9 bar. All cool details about the protection from this cap can be found over there (recommend to read!). 


● The 164cc Light Bore Piston is made just like all other Yuminashi pistons from AA-Grade aluminium and finished with a black molybdenum coating on the sides of the piston. The piston from this 164cc light bore kit has been developed to work in combination with the stock 125cc cylinder head and valves, hence the name Light Bore Kit and Light Bore Piston. 

The valve pockets in the piston are machined deeper compared to stock, and allow a 0.05mm IN / 0.08mm EX valve clearance. 

● The high grade Yuminashi piston rings are developed and produced by very strict Japanese standards and all rings are treated with a hard chromium plating layer (Cr). All details about the piston rings can be found over here.


● The YUMINASHI Billet CNC X250RR Camshaft Kit comes also with the ULTRA kit, and this cam is the hot ticket for getting the most out of your PCX125 V1 engine.

This Yuminashi camshaft is designed in conjunction with our racing efforts, and in turn the design gets passed down to our customers for the best power gains.

Yuminashi R&D designed this camshaft to be used in combination with the stock 125cc valves, with an increased lift and duration to produce a potent curve with solid torque to red-line. 
This means when you whack open the throttle out of a corner, you'll get a nice hit off the bottom all the way to the top!

All Yuminashi camshafts come standard with high-speed NACHI JAPAN C3 bearings to meet our standards concerning durability and reliability.

These high-end bearings can run exteme high RPM's, where the C3 stands for an optimal clearence with less friction at operating temperature.

The 2 special tappet adjusting bolts come with the camshaft in the kit because with the high lift of the camshaft it's not possible to use the stock tappet adjust screws.

**The valve clearance is 0.05mm IN / 0.08mm EX.



● The stock 125cc and 150cc eSP 12.95mm roller diameter is adequate for all stock camshafts, but high performance engines with high lift camshafts benefit from larger diameter rollers for the simple reason that the larger face of the 16.9mm rollers accept a more aggressive lobe profile before the roller digs into the cam lobe, which of course leads to nearly instant camshaft failure.

Therefor the rocker set with larger, more durable rollers comes together with the 164 ULTRA kit to ensure increased durability and reliability. 


● The special Yuminashi SPL Tappet Adjusting Screws which comes with the set will need to be installed if you install a high lift camshaft.

The stock Honda screws are shorter and you will face a problem to lock the stock tappet adjust screw.

The Yuminashi SPL Tappet Adjusting Screws have a groove to make easy adjustment possible.


 Keep in mind that installing a high performance camshaft with more lift and duration might affect the operation of the ISS Idle Stop Start system.

 ● The Progressive Double Valve Spring Conversion Set comes with the ULTRA Light Bore Kit for the power aspect, but also for the safety aspect since your engine has no RPM limiter anymore once the PMF-FI Controller is installed, and these double valve springs eliminate the chance on floating valves at high RPM entirely.

This kit includes 2 outer valve springs, 2 inner valve springs and 2 lighter as stock steel 5mm valve retainers to make a complete conversion from the stock single valve springs in to a double valve spring setup possible…


● The CR10EK Nickel Multi-Ground spark plugs have been tested in combination with the Yuminashi 164cc light bore kits, and the results are a cooler running engine with improved combustion, and clearly less sensitive for engine knock.

Multi-Ground Electrodes Improve Ignition Capabilities and Are Less Sensitive to Increased Voltage Requirements Due to Gap Growth.


● The 164cc Flat Deck Cylinder is pure racing DNA from the YUMINASHI PRO-SERIES.

The Flat Deck cylinder has larger water/coolant capacity, and is developed by the Yuminashi R&D to have a cooler running engine.

With the flat deck design you are able to run higher compression ratios without the fear of blowing head gaskets. A very hard cylinder sleeve has been installed which comes directly from the Yuminashi racing series engines to avoid ovalisation, oil leaks and compression loss!...

This specific cylinder block 12100-KWN-600X has been prepared to be plug & play ready for the first generation PCX125 crankcases. The crankcase bore is smaller from the first generation PCX125 compared to the eSP PCX125's, so the cylinder has been developed in such a way to make a plug & play install possible. 

This cylinder block comes also with the 3 pins to connect the stock ignition coil bracket on the cylinder, which is also unique for the first generation PCX and with a 125cc mark on the cylinder so that there isn't any difference compared to stock once the cylinder is installed on the engine.


● The special copper 0.3mm gasket set is made to make a perfect fit with the stock 125cc head in combination with a 60mm bore on the first generation PCX125 high compression engine (164cc kit). These copper gaskets come with the kit to make sure your engine makes the perfect seal. (Click the image below for more information)


 ● The large diameter Big Tube Air Intake Set for the 31mm throttle body which comes with the kit make sure your engine get's the air it needs to make the most power out of it, (more information and pictures can be found over here).

Keep in mind that the diameter of the hole in the stock PCX125 air filter box will need to be modified, and the length from the Big Tube Air Intake will have to be shortened based on your needs. 




 Free worldwide shipping with DHL Express is included in the price quotation!..
(Exception for Russia, Portugal, Brazil, Canary Island and French Polynesia, they will be served with free shipping by the Express Postal service)




- THE PCX125 LED (2014-2015)
- THE PCX125 SMART KEY (2016-2017)
- THE PCX125 DIGITAL (2018- )


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