MNSBR: Super Grom Build - MNSBR

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Super Grom Build

#46 User is offline   POE Icon

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Posted 13 June 2018 - 03:32 PM

View PostnOOb, on 13 June 2018 - 03:26 PM, said:

Yea the unfortunate thing is that a fuel controller and its other components costs just as much as the kit itself. Are you sure the stock O2 sensor is sufficient?

I'm tempted to just run a BBK if I'm spending $500+ on a fuel controller and wideband sensor.


Stock O2 sensor is a narrow band sensor and it's installed in the head in the exhaust port. Stock ECU uses it just fine.

If I would have known I was getting in this deep with the kit I would have researched BBKs more first. But the reliability is a problem with BBKs.
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Posted 13 June 2018 - 03:42 PM

I'm still thinking I must have setup something wrong. It just doesn't make sense to change this much on a motor and have such a minimal gain. I understand it's only 125cc, but still.
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Posted 14 June 2018 - 09:54 AM

The last few rides I've thought that, yes, it does have more power, but just not as much as I would have expected. I imagined nearly doubling the horse power (supposedly) would carry more than 60mph sitting up. I could already get 55mph sitting up on a stock motor.
I also need to consider the fact that I have not ridden a stock Grom in a few weeks. I should take out my stock Grom for a rip and compare the feeling to the built Grom. I still think that won't explain the dogginess of the new build. It's either something put together wrong, or trying to make the stock (but highly modified) air box work is effecting things more than I can imagine.

Here's the plug:

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Posted Image

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Posted 15 June 2018 - 08:13 AM

Revealing update:

I rode a buddy's Super 125 Grom that was put together with a Power Commander 5, wide-band O2 sensor, custom map and ignition module. Basically all the high end crap I really didn't want to pay for.

Result: I rode his Grom, got onto the first open straight and cracked it open. It didn't blow my mind, but had some very serious low to upper-mid range grunt that mine is lacking. The top end (9k-12.5k redline) was very similar. He had stock gears where as mine are currently -1/+1, but I figured that into what I was observing. Sitting up on his Grom, I was not able to get to a true 60mph, probably 58. It was windy, but still couldn't get up to 60 after we turned around. His Grom definitely has the hole shot and middle power I'm craving.

One more note before my conclusion... I took the front airbox cover off this morning and just screwed the Koso high-flow filter directly to the box so there would be no air flow impedance from the cover. It made no difference. This air filter should have very minimal flow restriction.

Conclusion:
I need a fancy expensive fuel controller to get my idle-9k power that I expected. I didn't want to be 'that guy', but if I'm in it this far, I might as well do it right. I won't buy it right away, but I'll eventually get around to it. I wouldn't doubt it if I put it off to winter or next spring. I'm still at about the same low end power as the stock engine, but mid range is a tick more. I'll get this thing geared properly for the power I do have now and it will definitely be a solid improvement overall.

Recommendation:
If you have the desire to build a little bike, the Super 125 will get you some good results if you pay for the fancy computer and maintain some very solid reliability. This just comes at a higher cost than a BBK.
If you went BBK, you would sacrifice reliability, but get cheaper power gain and likely have more low-mid torque, which is what I miss. I like wheelies, so the torque would be nice. But at least I know I'll have the low-mid power back once I get a real fuel programmer.

If I know you, feel free to ask for a test ride if you're curious about this build.

Anyone know much about the ARacer RC Mini 5 vs Power Commander?


No front airbox cover

Posted Image




Changed up the color. Hindle exhaust looks good. I heard someone else ride it yesterday and it's not as loud as I imagined it to be (w/ baffle), but it's still loud.

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Posted 15 June 2018 - 08:30 AM

Can your friend hit 60mph? Im curious of rider weight? Im getting that Rs2 yoshi system. Think he is throwing in ear plugs too haha. I will have to toss the gps on it after to figure out my top speed again.
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Posted 15 June 2018 - 08:32 AM

Do you think your stock Grom would have anything from 9-12k (in 3rd)? Assuming that the rev limiter was raised? I'm trying to sort out something on my Z, but don't know anyone else with a Z to compare it to... so Grom is probably 'close enough'.
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Posted 15 June 2018 - 08:47 AM

View PostVrooom, on 15 June 2018 - 08:30 AM, said:

Can your friend hit 60mph? Im curious of rider weight? Im getting that Rs2 yoshi system. Think he is throwing in ear plugs too haha. I will have to toss the gps on it after to figure out my top speed again.

He's 250lbs. He said he can get over 60. I'm sure that's with ideal or beneficial conditions. His 4th gear was stalling out at about 7500 - 8000 rpm and not accelerating. If he gears down, his bike will be a beast.

View Postcrakerjac, on 15 June 2018 - 08:32 AM, said:

Do you think your stock Grom would have anything from 9-12k (in 3rd)? Assuming that the rev limiter was raised? I'm trying to sort out something on my Z, but don't know anyone else with a Z to compare it to... so Grom is probably 'close enough'.


Stock redline is 9500 rpm. So no, not pull much there. If the limiter was raised on the stock bike, the power starts to drop off after 9k, so it wouldn't matter much. I believe that to be an issue with air flow on the tiny diameter intake/exhaust. But, 3rd gear on stock Grom still accelerates through the entire range in neutral road/wind conditions.

One more thing I'm considering is going back to a stock 420 chain and sprocket setup and sell the 428 as slightly used. A couple big shot grom mechanics said the extra weight of a 428 isn't necessary. If you buy a high quality 420 chain it won't stretch with the type of power this kit makes. The lighter rotating mass will help free up some power. And I got to thinking, if dropping from a 530 or 525 down to a 520 is useful on a big bike, dropping from 428 to 420 should be a measurable difference.
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