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Discussion Starter · #1 · (Edited)
Not sure if I should start from the start or from my latest mod.

This is my Yellow Monkey. It was from the first shipment of monkeys to Australia in July 2018.
By August 2019 it had 12hp as a cammed 125. In June 2020, I made it crazier and upped it to a 4 valve Takegawa 181. Now it's run in and its a rocket!

Stay tuned for more details. I have plenty of build pics and details to share.

**EDIT - Post #19 is where the 4v upgrade starts

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Discussion Starter · #7 ·
be careful with the Takegawa 181-4v engine, their pistons are junk, "cast made" and they come a part at high rpm range when the heat on the cylinder gets up to the 290-310F range. I'm having JE piston build me 4 custom made 181-4v forged piston to Takegawa specs.
Can they make 5? What are they worth?

I'd be keen to keep one as a spare and chuck it in the bike when I get around to porting it.

Is that 290-310f cylinder temp measured using the stock sensor or and additional sensor on the clutch side of the cylinder?
 

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Discussion Starter · #9 · (Edited)
Anyway.... back to the original thread.

First mod I did in 2018 was a GCraft Tail Tidy. Not really much else was available for the monkey at that point, unless it was a pre-existing grom part. The GCraft tail tidy is a decent quality item which retains the oem plate light and allows tilt adjustment. The bolt spacing is much narrower than an Australian plate and as a result, my number plate is fully cracked in 2020. I've ordered new customised "DK0NG" plates and I'll be sure to cut a plastic backing plate so that the vibrations don't crack my new plate.

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Discussion Starter · #10 · (Edited)
Next round of mods in Late 2018/Early 2019 were the diy shifter linkage, tool-less seat screws, exhaust, intake and injector.

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As we all know, the stock link is sloppy as. Since the holes for the stock linkage is 7mm, it's the perfect size to tap an m8 thread. My shifter linkage is made from m8 rose joints. Since it's directly bolted into the shifter plates, it has a very direct feel, but it still retains the same range of motion and leverage as stock. I've ridden friend's monkeys with the KX65 shifter and no linkage, and I didn't like the short and stiff feel.

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The tool-less seat screws were made by Level Up in Australia. They give easy access to the battery and electronics and fill in the massive frame holes that the monkey has for the seat bolts

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I got fed up waiting for a monkey intake and got a second hand Grom Chimera and a new Sprint Filter. Massive improvement from the stock airbox. I did run into some issues with the wiring for the IAT (Intake Air Temperature) Sensor, since the wires on the monkey are a bit shorter than the groms. I ended up cutting the wrapping on the wiring harness, seperating out the IAT wire and then re-wrapping the rest of the harness. It just reaches after doing that. Chimera now includes an IAT extension plug in the monkey kits, so this is just something to keep in mind if buying second hand.

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For the exhaust, I got an Aodonly Racing pipe from Thailand. At the time, the only high pipes on the market were the Aodonly Racing and the Yoshimura RS3. I must admit, the AR is a really good sounding pipe for the money. I wouldn't hesitate recommending it for any stock bore monkeys. Now that I am 4v, it's quite restrictive.


With the intake and exhaust installed, the bike going to run lean in the open loop fuelling. To compensate for that until I got a tuner, I installed a PCX150 injector (Honda PN: 16450-KZY-701). Weirdly enough, the cheapest way to get this in Australia is actually from a Honda dealer, for only 40 AUD. There's a lot of debate on here about the merits of using a pcx injector on a stock bore, so I'll go into detail on that in my next post.
 

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Discussion Starter · #12 ·
What I observed after installing the PCX injector without a fuel tuner.

After resetting the ecu and doing 40kms, the ECUs adapted well to the changes. For minor changes like exhausts, intakes and injectors, the stock ecu changes the fuelling in the 0-80% throttle range until it achieves an afr in the low to mid 14's. So if you're bike is sputtering around after you change the injector like mine did.....just keep riding. It'll adjust. Same goes for leaning it out from an intake/exhaust.

The issue comes with the 80-100% throttle range. The ecu only compensates for the air temp sensor in this range and interpolates the long term fuel trim from the <80% readings. This is the main reason I put the pcx injector on my bike. If you put an exhaust and an intake on, the bike runs leaner than stock at 80-100% because the bike is running as if it was stock. If you put a bigger injector it runs richer because the same % of an injectors max flow rate is getting called up by the ecu. In my case, it overcompensated for the intake and exhaust and made it a tad too rich. One other thing to note is that the maximum negative long term fuel trim is 36% on the stock ecu, so installing a PCX injector (56% more flow than stock) will make your map ~20% richer.

At the time I hadn't gotten an aftermarket ecu, but the pcx injector was only $40, ran safe and future proof for future mods.
 

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Discussion Starter · #13 ·
Next up were some smaller handling mods.

Swapped to Michelin Power Pure SC's with 120/70r12 front and 140/70r12 rear. This changed the feel of the bike more than I thought it would. The bike is a lot more twitchy and tips in more enthusiastically than stock. For reference, the stock monkey tyres are bigger than the stock grom. Monkey Vee Rubbers are 120/80r12 front and 130/80r12. The other monkeys that I usually ride with are running 130/70r12 front and rear, 130/80r12 front and rear, or 130/70r12 front with 140/70r12 rear.

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I also put some 3D printed shock spacers in the stock rear suspension to stop it from bottoming out all the time. Me and another Sydney rider tried 10, 15 and 20mm spacers. For a 100kg rider, 10 is on the softer side and 15 is on the stiffer side, but both work well. 20mm is far too much for 100kg. The inserts fit under the top bell housing on the shock, so they aren't visible. Mine are still holding up well after ~3500kms.

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Discussion Starter · #14 ·
Stock chain is made out of cheese, so I converted to a 428 chain and sprockets.
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My monkeys got klx125 front sprockets (jtf273 or rk 3122) and Honda cg rear sprockets (jtr269).

14/34 gave good acceleration and reduced bog off the line, but ended up revving way too high for my local roads. In my area, roads are generally 80-100km/h.
15/34 is same as stock, and ended up being my pick when it was still a cammed 125.
16/34 is too tall for the 125, but I'm really loving it for big bore. Now it cruises at 100km/h at an easy ~6700rpm

To compensate for gearing changes, I got a 12oClockLabs SpeedoDRD. At the time, there was no monkey version available, so I got a H8 unit for the grom, which didn't work initially. After some emails with 12oClockLabs, I rearranged the pins in the tail light connector and got it working. SpeedoDRD have since released a H9 unit for monkey which is plug and play. Its a good unit and priced reasonably.
 

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Discussion Starter · #15 ·
After 1 year of ownership, it was due for a service. Since the side cover had to be removed for a spinner clean anyway, took that opportunity to install a Kitaco clutch cover, oil pump, clutch springs and clutch lifter. I also installed a Kitaco type 2 cam since I'd be doing valve clearances anyway. I used a 5c coin to lock up the gears and it fell into the crankcase since I'm a retard. After a lot of lifting and shaking the bike, I got the coin out and now I make sure I use a 20c coin so it doesn't fit in those oil holes.

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To control the fuelling, I got a Dynojet Power Vision 3. Initially, I was using it without a wideband unit and just tuning by feel like I would on a carbied bike. I have the wideband unit module now, and it does make it a lot easier to squeeze out a bit more power. For a cammed 125, you can get away without the wideband, as long as you're not trying to break any records. For a big bore, the wideband is a must.

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Discussion Starter · #16 ·
The Kitaco Type 2 Cam really woke up the bike. The type 2 favours high rpm and peak power (12hp) was at 9000rpm with the stock porting. Makes good power without needing to rev it to the moon like the TB Cam. The Kitaco gear doesn't seem to get used much by the US riders, but its seriously good gear. For us Aussies, TBolt and Koso parts usually end up the same or more expensive than the equivalent Kitaco/Takegawa.

 

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Discussion Starter · #17 · (Edited)
Not really a performance enhancer, but still a nice little part of my map. The PV3 lets you modify the rev limiter on AND off revs.
The stock map and all of the pre-made dynojet maps have the "hysteresis off" value set 250 revs higher than the "hysteresis on", which gives the grom its bob-bob-bob rev limiter.
My maps have the h-off value set only 100 revs higher than the h-on to make it sound a bit more dirt bike-y.


Clip 1 - Stock 9250rpm rev limiter with hysteresis on/off 250rpm apart. The classic Grom bob-bob-bob sound on the limiter
Clip 2 - Stock engine, 9400rpm rev limiter, but with hysteresis on/off at only 100rpm apart. Aim was to make it sound more like a dirt bike.
Clip 3 - Takegawa 181 4v engine, 11700rpm rev limiter with hysteresis on/off only 100rpm apart. Actually sounds like a dirt bike now...
 

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Discussion Starter · #19 ·
Now the part that everyone is waiting for....

My original plan for this bike was to wait until after my wedding and then get a kitaco neo kit. In April 2020, my wedding got cancelled and postponed to 2021 due to COVID-19 restrictions on gatherings and venues. Now that it was ages away, I figured I could do my big bore early. I fire up webike and as it turns out, Takegawa just released a silver version of the 4v 181 kit and webike had it for 20% off on the same week that my wedding got postponed. Timing was perfect, so I ordered the Takegawa 4v kit and the new Takegawa crank. Unfortunately, air freight from Japan was suspended, so I had 6 weeks of waiting in anticipation for my sea freight. For reference, at the 20% off sale price, this made the Takegawa 4v kit cheaper than a Koso 4v 170, when delivered to Aus.

There hasn't been much information about the Takegawa crank and I've only seen 1 other build from an English speaker that uses it. Looked like a decent enough kit, with a chunky looking crank, reinforced cam chain and new stronger woodruff keys. Given all the issues that people have with the woodruff keys, I thought this was a good addition.

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Discussion Starter · #20 ·
The monkey looked a lot emptier than usual....
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The takegawa crank is one beefy unit. The crank webs and rod are much bigger than stock. I didn't weigh the cranks, but my impression from handling them is that the takegawa crank is heavier than stock. I was hoping that would be the case, since I wanted to bring back some of the crank inertia that I lost when I removed the spinner.

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4v vs stock head. Valve area has doubled. Stock is 25.5mm in and 21mm out. The takegawa is 2x25mm in and 2x21.5 out

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Discussion Starter · #21 ·
To remove the OEM crank bearing from the case I used 2 sockets and a cup head screw. The cup head screw locked into the 1/2 drive on the socket, so I could tighten the socket down against the inner race of the bearing. I then put a much larger socket over the smaller socket, so there was a large flat surface. I then gave it a few careful hits with a mallet to pop out the old bearing.

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To get the new crank bearing in, I froze the bearing and heated up the case. Even after doing that, the bearing only slid in half way before getting stuck. To get it all the way in, I put the old bearing on top of it, and used a socket on the inside of the bearings as a locating pin. I then carefully tapped the outer race of the old bearing, working my way around the perimeter until the bearing was fully seated.
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When it was time to install the crank, the heat and freeze method didn't work at all. Tbh, the only good way of installing the crank into the case half is with the proper crank puller tool. Luckily I have a local Kitaco/Takegawa importer who had the tool in stock.
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A few of tips for anyone doing this:
  • Buy a box of resealable sandwich bags and a sharpie. As you disassemble the engine, label the bags and group the components
  • Take lots of pictures, especially the order that things sit on the crank and transmission input shaft
  • When you split the cases, use 2 rubber bands to stop the transmission falling out
  • Lookup Honda Grom Parts Fiche before you start to disassemble the engine. Make note of small dowel pins.
  • The engine can stand up on its own if you use M8 bolts and washers in the 4 holes on the bottom of the motor
 

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Discussion Starter · #23 · (Edited)
For the throttle body, I'm using a 34mm Honda Vario scooter throttle body. At 35usd, it's a steal and shipping from China to Aus is much cheaper than USA to Aus. You'll need the koso manifold to fit it, but I got one of those really cheap from a friend that bought a gf rev wedge.

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Already comes ported and polished

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Sensors are the same as the monkey/grom

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Weirdly enough, the new throttle has the same bolt spacing as the stock throttle, so I had to modify the koso manifold to fit. Bolt holes were reamed out, the top corner was notched in to make room for the iacv, and the side was ground down slightly to make room for the return spring. Also, the cable guide plate from the stock throttle can be swapped onto the vario throttle to retain the oem cable protector plastic.

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Yes it comes with the infamous brass screw

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Since I had bought the koso manifold second hand, I had to bore out my stock insulator and find a new injector seal ring. I ended up with a Nissan SR20/RB26 injector seal

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Discussion Starter · #24 · (Edited)
Next issue is my injector woes. With my old pcx150 injector, it would fire up straight away and throttle response was great. The issue was that the duty cycle was above 85% from 8500rpm and above. At 11300rpm, the duty cycle was 100%.

I've ordered the Forza injector 235ccm from Honda, but it's on backorder due to the Covid situation. Until it gets here, I've got a 180ccm 14 hole yuminashi injector that someone was using for an E85 grom.

The bigger injector is giving me some tuning headaches. Cranking fuel had to be turned way down, since it was fouling plugs on startup. I'm still experimenting with throttle tip in enrichment. My in gear enrichment is now working well, but the neutral/clutch in enrichment is still too rich. A sharp crack of the throttle will stall the bike in neutral. This is actually kinda dangerous when rev matching on downshifts. Main table fuelling is easy to tune with the wideband, but these finicky bits like warmup, cranking and tip in are just trial and error.

For spark timing, I'm using gsx/jc's timing table and it flat out rips. The pv3 was artificially limiting the spark timing at first but now I've changed the limiters to allow 27 degrees btdc at high rpm and 100% throttle
 

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Discussion Starter · #27 ·
So for people with a stock bore running an exhaust and intake with NO fuel controller, to prevent running lean or too rich at WOT they would be better running this 120cc injector instead of the 140cc injector you ran?
Yeah that's right. There's another Sydney rider who uses that injector. The 120 is good, but the 140 is cheap and readily available from Honda.

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Discussion Starter · #28 ·
Next upgrade is an Over Racing Exhaust. Webike has them on sale for 17% off today.

One of my other monkey buddies has the Ti version of this pipe, and it has a nice large header (28mm at the flange and tapers up). The SS version that I'm getting should be the same size, but I'll report back once I get it.
 

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Discussion Starter · #30 · (Edited)
I've upgraded the ignition coil to an aRacer Power Spark Red. It has adjustable spark energy levels (1-9) which is kinda reassuring when you're so far from stock. It says to use 1-9 for stock motor, 1-6 for a 155cc big bore and 1-4 for a high comp motor. I've got it set at 3 at the moment and it seems to be working.

Not sure if this is helping up top. The bike runs out of puff at 10500rpm. Not sure if its held back by the 10d cam, the standard porting or my tiny exhaust (still haven't received my Over Racing pipe). I did notice that the idle is a bit more stable and its a bit cleaner off the bottom. I guess thats a win?

It bolts up fine on the stock coil mounting holes, but the terminals end up the opposite way around vs the stock coil, so make sure you check the connectors if you;re installing one of these
 

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