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Discussion Starter · #1 ·
I bought my first Grom new in 2015. There wasn’t much back then in the way of builds. Mostly big bore was it. I sold the bike after 2 years and still regret it. Fast forward to now. I bought a 2020 Monkey. It suits my riding style well and I can’t see ever letting it go. It brought back a lot of memories of what I felt was wrong with my stock Grom. My guess is I’ve put about 6k miles on the 2 combined.
on the Monkey I installed the Takegawa sport exhaust, Chimera intake, Tb cam, and a Cameron Jones ECM. I tested gear combos and settled on 15 front and 37 rear. It increased 4th gear top speed and felt better in 1st. I also installed a 12oclock speedometer healer. I’m 200# and it could get me up to about 63 mph top speed. More important to me was the ability to be able to do 55 when I had to for short 3 or 4 mile bursts even up hill.
I was very un happy with the build and one by one I started removing the mods. First to go was the chimera intake. I hated the noise. For me it took away enjoyment riding it. I lost some top speed. Next was the Takegawa exhaust system. I really like how quiet the bike is stock and even though the Takegawa wasn’t loud, stock was quieter and I like that, I lost more top speed. After a few weeks I went back to the stock cam. I preferred the power band the stock cam offered over what I thought was a louder cam forcing me to keep the revs up for power. Yup I lost speed again. I pulled the Cameron Jones ECM and went back to stock. For my weight and road conditions I can barely pop 56 mph top speed and when it counts and I need a burst of 55 mph I can’t always get it. 52 is What I can count on. All of my modded parts were sold here and I’m back to square 1.
My honest evaluation is it’s great like it is if all I wanted was 45 mph, but I don’t. I think an important part of any build is not just how big but also how enjoyable is it. I’ve come to the conclusion that a big bore 181 is not anything I want. The supporting mods like intake and exhaust requirements would make me not like how it rides.
I have built a few older CT70 motors and my favorite is a 124cc with a stroker crank. It is faster in all gears and at top speed (69 mph). More important is that it can run 55 mph when I need it to. That has me wondering about what kind of build is possible for my Monkey. if I’m completely honest here I will have to say I want to keep my stock intake and exhaust. But, I need to bake in another 10 mph.
Here is where I’m going with this rambling. Is a 143 build with stock intake and exhaust possible? What would the fuel injector requirements be? What is the best way to manage the A/F ratios and heat? Would I get the 10 mph I’m looking for? Will it even work? I really don’t care what top speed is possible I care about keeping the bikes characteristics similar but moving the needle up by about 10 mph. I know there’s more than a few folks here that have some super builds and I’m hoping to hear some honest thoughts. Thanks
 

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Sounds like you should keep the bike stock since you didnt like the mods. 143 isnt that much better either. I would reccommend that you go with a 164cc bbk and TB cam and intake with the Aracer to get the most out of it. If you want an exhaust that is quite then look into the mugen exhaust. I have a ported head TB cam and koso 34mm TB and larger intake pipe and stock airbox with the koso filter and its not bad and all stock i could hit rev limiter in 4th
 

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Discussion Starter · #3 ·
Thanks for jumping in. I’m not I interested in going that route. I think it’s almost perfect stock. I just need a few mph so I can get on roads that have a. 55 mph speed limit. For me WOT does 52 on a few hills that I need to be going 55 on. I was hoping that the stock intake and exhaust could handle the 143. A fuel management and oil cooler system wouldn’t bother me neither would a high quality cam if it isn’t a regrind, but aftermarket air intakes and exhausts do. Appreciate hearing from you.
 

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I'd do a koso intake hose, panel filter, DHM throttle body adapter, Takegawa cam or the likes. I had that setup with an exhaust and it ran closer to what you are looking for. I think the cat hinders stock exhaust might be what will hold you back. That cam falls flat up top but pulls well through the mid range enough to feel like a high comp piston set up revving to the stock limiter would.
 

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Discussion Starter · #5 ·
Can you comment on the amount of intake noise it made. The chimera I installed was as loud as the takagawa sp exhaust. I read a little and think it’s worth looking into. I will give DHM a call maybe David will be able to put something together that gets it where I’m trying to go. Thanks for the suggestion. I wouldn’t have thought increasing intake would do much without an exhaust. IDK
 

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You aren't alone! I absolutely love my monkey stock but would love 10 more mph so I can take it up to the mountains. Intake and exhaust are 100% out of the question for me
 

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You could run a 181cc with stock intake and exhaust. I don't believe you have to change anything either. The intake, exhaust, and cam are so restrictive that it will fill in some bottom and midrange grunt but with stock gearing probably won't net a huge speed gain.

You would need a gearing change to take advantage of the torque.

If I were doing a build to minimize necessary upgrades I'd go 143cc with Takegawa sports cam, do some slight intake mods at least so it can breathe and add an ARacer ECU to dial it in.

Probably wouldn't need an oil cooler.

Then gear it to suit your speed requirements.

Oh, a get a ported head on it.

I noticed a big change when that was added to my 181cc 2 valve.
 

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Discussion Starter · #8 ·
Thanks Chillis. I’m not going to throw parts at it and cross my fingers. Been there have the shirt. Your gearing comment has some truth to it. I tried 15/34 (stock). 14/34,15/35,14/15,15/37,14/37 I am running 14/35 it does not pull 4th gear to the limiter or even near it. I tracked down a 36 and plan to see if 14/36 would be the sweet spot. 14/37 made the bike very peppy but at the expense of being a little too buzzy for my taste.
a gear head friend suggested I look for a K&N filter before I look into any mods to the air box. His rational was reasonable since I’m only looking for a small increase in mph. And I dont want to hear the intake growling I’m going to do both at the same time 14/36 and K&N filter then see if I can pull 4th up a notch. I’m thinking a quality cam would be next if that doesn’t get me to my goal
 

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I’m running the much larger Koso outer snorkel, BMC panel filter, Koso connecting tube, and the DHM adapter. I personally do not believe it is any louder than stock. It is a great setup and I believe it flows very well. I have no desire for the additional noise of an aftermarket intake. I hate intake noise. That reverberating sound is awful. I doubt you would be disappointed using the Koso tubes. With that said, I have a 2018 Grom, so I’m not sure about compatibility with a Monkey airbox.

The bike has a ton of modifications, but not all of them contribute to additional speed, which is what you are after. The mods that do contribute are: lightweight Kitaco sprockets in 15x36 sizes, Kitaco clutch cover which removes the 2.5 pound centrifugal oil spinner from the crank, Yoshimura ST-2M camshaft, Kitaco titanium tappet adjuster nuts (meh, couldn’t hurt), Gromfatherz speed spacers (maybe they help), the Koso intake tubes, BMC filter, Anodizing Racing exhaust, and Cameron Jones Racing ECU reflash (10,000rpm rev limit). I’ve removed about 18 pounds from the bike, but added at least 3 pounds back on with certain parts. My bike is way faster than 55mph. I weigh 165 pounds currently. To achieve absolute top speed I have to tuck, but 55mph is nothing for it to achieve. Speeds between 65-70mph are not a problem when tucking.

The Kenda KD1 tires were about 1 1/2 pounds lighter than the stock IRC tires and the EBC rotors were about 3/4 of a pound lighter, if I remember correctly. I’d have to look at my photos of the parts on my scale. That is rotating weight.

The exhaust is probably too loud for you. It is very inexpensive. I paid about $87 dollars for it. After over 1 1/2 years, it pretty much looks new. I love the sound of it with the baffle in. Sounds like a real motorcycle. With the baffle out it is pretty obnoxious, but the bike is faster.

The Yoshimura ST-2M cam is awesome. It is not a regrind. I feel like I lost almost nothing on bottom end, but gained lots of top end.

My friend is running the same intake setup, same exhaust, same tires, TB cam, 14t front sprocket, DHM reflash, and a DHM high compression piston. My bike is still faster than his. We expected more from the high compression piston. He will readily admit that my bike is faster. No BS. We don’t know why exactly.

All I’m planning to do from here is taper boring the throttle body and maybe some mild head porting. I was going to do a big bore kit, but my bike still has Honda reliability and is plenty fun. I think I’m done for now.

Some parts probably add additional reliability. Takegawa super oil pump, Kitaco oil cooler, Takegawa 4th crankshaft bearing, Takegawa cam chain tensioner, Kitaco tensioner button, Kitaco machined aluminum clutch lifter plate with Kitaco 60% stiffer springs, etc.

I would probably skip the K&N filter and do a BMC, DNA, or Koso filter. I think they may have more intake area.
 
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Discussion Starter · #10 ·
Thanks for the post. There is a lot of info in it and plenty to consider I haven’t really thought about the weight of the bike as something to help. I’m especially interested in the clutch cover mod removing the spinner. Also thanks for the cam info. Every site I have been to talks their cam up but none really say what you can expect. I’ll probably re read this post a few times to absorb it and see if I can cross reference to the Monkey.
 

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Thanks for the post. There is a lot of info in it and plenty to consider I haven’t really thought about the weight of the bike as something to help. I’m especially interested in the clutch cover mod removing the spinner. Also thanks for the cam info. Every site I have been to talks their cam up but none really say what you can expect. I’ll probably re read this post a few times to absorb it and see if I can cross reference to the Monkey.
Let me know if you find anything about running a cam on an otherwise stock Monkey.
 

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Discussion Starter · #12 ·
I have a 36t sprocket to install and will try it with a 14 then 15t front sprocket. It’s the only useable combo I haven’t tried. I’m also going to install a better air filter but not do any mods to the air box. I’m only looking for 3 mph at this point. The cam is the hardest part. I haven’t been able to find good real world reviews on a 125 stock setup. Lots of technical info out there even on this site but that’s not useful to someone like me. Eventually I will have to make my best guess and cross my fingers
 

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I think I ran a takegawa cam on a panel filter modded airbox, stock head, but had exhaust and a tuner to compensate for the air flow and power curve shift.

I think I got to 68mph with it. Had good midrange power, choked up top, and 4th was only good to 6k ish. Head winds could still slow me down. Before the cam and exhaust I struggled to maintain 45mph up a very slight incline with a head wind.
 

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Discussion Starter · #14 ·
That’s what I’m afraid of. I’m fine with the stock performance but can only get 52 on a reasonable incline. I really need that few extra mph. I hope the gearing can do it maybe even a few more miles to loosen up the motor. I won’t be changing intake or exhaust. A cam is a possibility for me but it would have to be a quiet cam. Not one I can hear slapping around in the head. And not one that requires me to be above 7k rpm to buzz around
 

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Discussion Starter · #15 ·
Help here please. Koso or K&N air filter. I really don’t understand how to compare them. The Koso is foam and the K&N is pleated. That’s all I can say about them. Is one really better that the other???
 

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Help here please. Koso or K&N air filter. I really don’t understand how to compare them. The Koso is foam and the K&N is pleated. That’s all I can say about them. Is one really better that the other???
Probably the Koso and there are a couple of others out there too you need to investigate.
 

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Discussion Starter · #17 ·
Thanks, I went with the Koso mostly because it was a similar material to a uni I use on another bike. I ran the gears 14/36 and it was a little buzzy for me. 15/36 was much nicer. I finally hit the rev limiter in 3rd. I was going about 57 mph. 4th wouldn’t pull past 53. I’m going to settle on 15/37t. It seems to do the best on the roads I ride. i was looking at clutch covers next mostly for the elimination of the oil spinner. It’s a mod that doesn't bother me because It may help the motor rev quicker without the spinner but won’t take away from the quiet ride I like. im asking if anyone added one with the stock exhaust. I know there is an issue with exhausts and the upgraded cover but don’t really know what is being said in the description. Which one will work On the Monkey I do prefer the silver over black just because the rest of the motor is silver
 

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FYI, some people comment on a noise after the spinner delete. I personally never noticed it, even before the new intake and exhaust. Just wanted you to be aware.
 

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FYI, some people comment on a noise after the spinner delete. I personally never noticed it, even before the new intake and exhaust. Just wanted you to be aware.
Yeah, mine sounds a little bit like a turbo whine. I am very sensitive to changes in sound. I play the guitar, so that is a good thing.

I will get in someone’s car and tell them, “You have a wheel bearing going out”. They say, “No I don’t. I don’t hear anything”. A couple of weeks later they tell me, “My mechanic says I have a wheel bearing going out”. I say, “I told you so”.

I got in my wife’s car one time and said, “What is that thumping sound”? She said, “I don’t hear anything”. I get out to look and there is a belt sticking out of the tire. I say, “Really? Couldn’t hear anything, huh?” lol...

The clutch cover sound doesn’t bother me at all. I never even notice it now that I’m used to it. After I first installed the cover, I was concerned that something might be wrong, but once I found plenty of other people who said their bike did the same thing, it put my mind at ease.

I wasn’t aware of fitment issues on the Monkey with the stock exhaust.

Does the Koso air filter show the red material around the outside perimeter, so that it is visible on the outside of the airbox?
 
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