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Old 11-05-2013, 01:42 AM   #1 (permalink)
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Honda MSX125 "Grom"

I'm a huge fan of Honda's horizontal singles and said for years if they ever came out with another street-legal model that used a version of this motor I'd buy it.

Last June American Honda announced that the United States would get the fuel injected MSX-125 (called the Grom in the U. S.) and I had to put my money where my mouth is and put a deposit on one. As it turned out they are in short supply with most dealers getting two and the first run of them totally sold out.

Reports started coming in on the MSX-125 web sites that folks in the U. K. were getting over 120 MPG out of these bikes. Mine finally came in and while my opinion of the bike in general is mixed the fuel mileage is indeed extremely impressive. So far my best mileage has been just shy of 127.

Has anyone else here purchased one? If you have what's been your experience?

Mine is happiest running at about 45 MPH and tops out around 55. Supposedly something as simple as intake modifications and an aftermarket exhaust system will take the top speed to nearly 70.

The motor is incredibly smooth with almost an electric feel to it. So far the F. I. system has been flawless and the little bike just starts and runs perfect. It would be very interesting to fully streamline one of these bikes and see what kind of numbers could be achieved.


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Old 11-05-2013, 09:10 AM   #2 (permalink)
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MSX125 | Honda/2013

Most likely you could get higher speed with changing the sprockets, my old Honda cb125 would do 60mph after changing sprockets.

What is the cost on a motorcycle like this? I haven't seen many new motorcycles that I would be willing to buy, but this one looks amazing!
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Old 11-05-2013, 10:15 AM   #3 (permalink)
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Theoretically $2999 MSRP but they're totally sold out. Some people are trying to make money on the bikes they've bought, asking four grand or more.

Unfortunately the top gear in the bike is an overdrive and you already can't pull redline in it. Gearing it up would make it unridable for town use.

Rumor has it that they offset the crank in relationship to the cylinder like they did on the NC700X. It also has a longer stroke than bore unlike every other horizontal Honda single, again like the NC700X. Could this be one of the secrets to good fuel economy?

One reason the engine might be so smooth is that the crankshaft is now supported by the right sidecover.

I know I definitely don't baby the bike and it likes RPM. I'm curious as to what kind of lifespan this motor is going to have and by it's electric feel I'll bet it's going to last a long, long time.

For my taste it's too much like a street bike with lots of bodywork, high-tech dashboard, etc. and it's heavy for what it is (225 lbs. wet). I'd much prefer a dual-purpose version with molded color plastic. It's a typical Honda, though and has an extremely polished feel to it.

Cycle World did a writeup on it and totally ignored it's gas mileage, instead sending it's dirt bike tester to a skate park to thrash it. While a good portion of these bikes are getting heavily customized and the vast majority of the youngsters who own them will use the bikes as toys the little buggers do have a very practical side.

I'm 5' 6" tall, weigh around 155 and the ergos fit me very well. The seat sucks, though--as is typical of the manufacturers it slopes far too much to the front and badly needs to be leveled out. If it was flat they'd lose sales because really short people would straddle it in the showroom and not be able to touch the ground. The foam is also hard as a rock. I bought a second seat and will likely send it to Sargent for a redo.

The front fork is too soft but various fixes are already available, from preload adjusters to high-end total rebuilds. The shock is a throwaway unit but for my needs works pretty well.

Once supply catches up with demand these little bikes will be an absolute bargain and excellent cheap transportation. Those interested in building a high MPG bike ought to be watching for a crashed one. With this kind of MPG out of the box imagine what it'll do with some streamlining!!!

Last edited by woodsrat; 11-05-2013 at 07:36 PM..
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Old 11-05-2013, 06:08 PM   #4 (permalink)
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If it feels smooth as an electric yet tops out at a mere 55mph, the gearing will be on the short side.

I wouldn't change the intake or exhaust, but make the gearing a bit longer and sacrifice acceleration for higher speed and lower rpm throughout.

I'd expect a modern 125cc to top out around 65-68 mph.
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Old 11-05-2013, 07:31 PM   #5 (permalink)
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Trust me, fourth gear is just too tall for the output of this motor. Hit a headwind or any kind of hill and your speed and RPM starts dropping like a rock. The aftermarket has already responded to this problem, too--Yuminashi makes a lower 4th gear that helps a bunch. The problem is who wants to split the cases on a brand new bike to install it???

What the motor needs is a 5th or 6th gear and I sincerely doubt we'll ever see that.

Several guys are making their Groms hit the redline in fourth and increasing their top speed by dropping to a 14 or even 13 tooth countershaft sprocket. The problem there is it shortens up the other ratios as well. I bought a 14t. and the gizmo to correct your speedo since it's driven off the countershaft but after getting over 120 MPG decided to just leave well enough alone.

Installing a 150cc kit supposedly gives you enough power to pull fourth gear to redline but honestly I spent enough time and money building XR/CRF-50's for backyard adult pit bike racing (there's a stupid expensive one in the garage as I write this that I'll never get any money back out of) and nowadays all I want to do is just ride 'em.

Doing something about the wind drag would really help--and that's where you guys come in. Starting with a bike that already gets fantastic gas mileage puts you way ahead of the game. It's cheap enough that you wouldn't mind cutting it up especially once enough of them get into the used bike market and their prices drop.

Last edited by woodsrat; 11-05-2013 at 07:38 PM..
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Old 11-06-2013, 12:52 AM   #6 (permalink)
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Originally Posted by woodsrat View Post
Theoretically $2999 MSRP but they're totally sold out. Some people are trying to make money on the bikes they've bought, asking four grand or more.
Anyone in the Northern states could check at a Canadian dealer if you can't find stock down there. We tend to not buy motorbikes in the winter, and MSRP here is $3199, but around December you could probably get one for a lot less. We have to clear room on the showroom floor for the snowmobiles, eh?? ha ha
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Old 11-06-2013, 11:05 AM   #7 (permalink)
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Looks pretty nice and the price is right. Wait a few years and the price will be even more right. It reminds me of my Dad's Honda 65 that is sitting in my garage... but a little more modern haha.
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Old 11-06-2013, 12:59 PM   #8 (permalink)
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Woodsrat, if you want to know what could be achieved with streamlining, take a look at Allert Jacobs' velomobile, there is a link from this forum. The motor in the MSX 125 looks to be the same as the one fitted to the european Honda Innova, which has been available in the UK for 10 years or more. Fuel injected, 125cc horizontal motor, 9bhp, the only difference is the semi-automatic gearbox (no manual clutch), which Allert converted to manual using homemade parts.
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Old 11-06-2013, 10:01 PM   #9 (permalink)
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I like the Grom for what it is. 9 hp might make it to 10 with a loud pipe which would give you another 3% on top speed.
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Old 11-06-2013, 10:17 PM   #10 (permalink)
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Wait a while, get one that is consmetically whacked up but mechanically OK. Then aero that baby and get 175 MPG! There will be plenty of them available in a year or two.


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