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Discussion Starter #1 (Edited)
So I’m new to the forums/Grom ownership and I bought one from a guy who had a shop do a KOSO 170 BBK + 4V Head install.
Well the bike likes to sputter and I've ridden other groms and this one doesn't feel any more powerful. Barely could hit 55mph in light wind and it sputters really bad in 2nd. I understand most motorcycle maintenance but inner workings of engines isn't my forte. I can usually figure out mechanical issues on my other bikes but this just seems over my head with all the mods. Plus I know a wrong turn can blow these engines with this mod.

The guy told me he got it dyno tuned and I'll attach the map that was on the PCV. But he said it has sputtered ever since the BBK was installed and he couldn't figure out why. He has the high flow fuel injector, NGK ER9EHIX, Hi flow oil pump, the Koso racing air filter, and a ZoOm full exhaust installed. So as far as being able to breathe, get enough fuel delivered, etc. I don't see where the issue lies. I have all the paperwork for everything he's ever done to it. He wasn't really a diy'er. More of a "take it to the shop" guy. So hopefully these have all been installed correctly.
I've scoured the forums for an idea but I really need to know what the next step is to get this thing running at peak performance with the BBK and just plain riding smooth.
My buddy said maybe they put low octane fuel in it and that's the cause. Plan on draining the tank and putting some premium in and see how it does. Thoughts?

Koso BBK_Zoom_aftermarket filter.jpg
 

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I think I would first check to see if the valve timing is not off. Check valve lash too.

I am not versed in the hows & whys of the PCV.

But...

What is your air/fuel ratio through out the RPM/throttle range? If the PCV will not give real time info, install a AFR that reads real time.

My two cents.
 

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Discussion Starter #3
Appreciate the info. I’m looking at getting a PCV auto tune now and from there seeing how it goes. In the mean time I’ll check the valve timing.
 

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OG or SF either way...
You should not have any fuel trims in anything other than 80/100% TP, unless its an OG and prevs owner did some wiring to eliminate O2...
0-60% should have Zero fueling.

Definitley get a Wbc2 auto-tune and Afr Gauge...
Fueling showing -60,,, Thats taking away alot of fuel for BBK and with no autotune someone has been tinkering...

Edit: correct my info on fueling
 

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Discussion Starter #5
OG or SF either way...
You should not have any fuel trims in anything other than 80/100% TP, unless its an OG and prevs owner did some wiring to eliminate O2...
0-60% should have Zero fueling.

Definitley get a Wbc2 auto-tune and Afr Gauge...
Fueling showing -60,,, Thats taking away alot of fuel for BBK and with no autotune someone has been tinkering...

Edit: correct my info on fueling
Yeah, I couldn’t find any WB2’s new so went with Autotune. Should be here this week. Gotta get the O2 bung welded then I’ll see where we are.

I haven’t messed with the original mapping. I loaded other maps and tried them but never changed any of the tables.

I wanted to check the compression but I can’t for the life of me find anyone who has a 8mm fitting for the compression gauge. How are guys checking their compression with these BBK’s?
 

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Looking at the map I'm pretty sure it has never ever been near a dyno!

Regarding the Autotune, if it hasn't changed, it's really not that good compared to the WB2. I'd cancel the order if still possible. You'll find more info here: DynoJet PCV / Wideband 2 Newb Guide
From that thread:

WB2 provides some features that the Autotune does not - including output to an analog or digital gauge (as mentioned earlier), and a narrow band O2 sensor output, so you don't have to use the factory narrow band O2 sensor that comes with the bike. This allows the WB2 in conjunction with the PCV to fool O2 sensor readings to the Grom ECU and allows the system as a whole to enrich the fuel map in the 0-80% throttle range (closed loop range), where the PCV itself can not otherwise make adjustment.

All of that being said, if you want to auto tune on the Grom, and you want to go with the Dynojet products, Power Commander V and Wide Band 2 are the way to go. There's basically no reason to go with the Autotune module sans to save a few bucks... but the extra features that come with WB2 make it more than worth the nominal cost difference.
 

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Discussion Starter #8
Thanks for all the help guys. Looks like the order for the autotune has shipped. For some reason my googlefu was off and I didn’t immediately find the WB2 for sale. I got the autotune new for $245 but I see they have the WB2 for $295 on amazon. I’ll see how things go on returns for the autotune.

Unfortunately we have new issues. I started up the bike and put 0 on all trims 0-60 and 15 on all 80-100. When I started up the bike, it won’t start without throttle help. I turned the air/fuel moisture screw all the way in and held the starter while unscrewing until it was all the way out. Didn’t change the failure to idle. And to add to that, the exhaust is puffing out white smoke. Doesn’t smell like fuel. When I tried to put it in gear and go a couple feet, bogged down and died.
Pulled the plug and there’s oil on the threads and a black sooty look on the plug.
My thought is all that running lean messed up the piston rings and now here I am burning oil and have low compression. Thoughts?

458896E0-D3E7-49D5-A235-B83A61601784.jpeg
 

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Discussion Starter #10
There’s 1300 miles on the engine but the guy said it was put on mid last year. Doubt he put that much mileage on it really.

Yeah, I was just stating I changed the fueling. Not that it’s what caused it to smoke and lose power. Getting a universal compression gauge fitting today or tomorrow so I can check the compression from that tiny spark plug hole. I’m assuming it’s going to need new rings.
I do have some questions though: Can I reuse the piston and just change the rings? What are indicators I should do the whole thing vs just the rings?
 

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Discussion Starter #11 (Edited)
So I followed the advice and canceled the autotune order and found a WB2 for about the same price.
I did a compression test today and came up with 180psi. Idk if that’s low or high for this BBK. Spark plug is still getting wet and black. I feel like it has to be piston rings but I warmed the engine and got 180psi for compression. I was expecting like 125 or something low.
 

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180psi seems good. Try pulling your intake manifold off and checking if the inside is all oily. If so, the oil is coming from the crankcase breather which is connected to the intake. I would vent this to atmosphere into some sort of catch can.
 

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Also, try adjusting the idle stop screw so that it just barely keeps the throttle body butterfly open. The air screw should be about 1.5 turns open. Once the bike can idle on its own, you can finesse it from there
 

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Wasting your money and time wih a PCV, seriously, go Aracer and never look back. All your problem will never go away until you get rid of the PCV.

As for the Koso 170-4v one of the best BBK kit

Compression looks good

I would recheck cam chain tensioner and replace it with a Koso arm and sprocket cam chain tensioner and also install the GFZ adjustable cam chain unit to replace the stupid OEM spring loaded plunger unit.

Not knowing what throttle body you have will give me limited things you should do for the intake side such as F/I size or changing it, and such.

that spark plug pic you posted shows it is running too rich or oil is getting on the spark plug some way. Black is bad so is white ash spark plug should be a light brown or tan/white color on the plug.

Did the last owner replace the throttle body with a koso 34mm throttle body, the Koso throttle body is usually black in color, stock is very small compared to Koso.

Take a pic of your engine with all the plastic removed so we can sort of analyze what should be done, make sure you take both the left and right side of the engine and with the airbox unit on and with it off so I can see what wires are connected plus I like to see the right side head to see if the OEM a/f sensor is still being used, if it is that is part of your problem.

Good luck, make sure to take some pic, a pic is worth a 1000 words
 

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Discussion Starter #15
Thanks for all the info guys.

Solidjohnny, I took the intake manifold off and besides a little black soot on my clean finger, wasn’t much in there.

Cisco, I pulled everything off and tried my best to get well lit pictures for you.
As far as fuel controllers, I’ll stick with the Dynojet for now and see how things go once I find out how the bike started smoking from the exhaust and the wetness on the plug. Looks like he did do the 34mm throttle body.

With the cam chain tensioner, is that something really needed? Or just would help. At this point I just want to get the thing running properly.

One thing I noticed taking all the plastics off. There’s a hose coming down towards the air box that wasn’t connected to anything. It has the hose clamp pulled back so I know it went somewhere. Maybe you guys can tell me where. Is that the cause of the problem? It’s the pic of me holding the hose. Made sure to get the pic of the right side of the head with the O2 sensor. Also took a pic of the top valves just for extra info. If any close up shots are needed, let me know. Lastly, I took a pic of all the stock parts that were changed out.
62208BF6-463A-4A3D-B139-33BA8D9045B7.jpeg 08645709-7F1A-450F-84B6-434220144FD2.jpeg 8A8FF548-0AA8-44B8-824C-97D8556FDC12.jpeg 7326651B-D290-4C0B-9A36-2D9DFCA29C2A.jpeg 7A168523-934D-43E3-A221-D0301A9F7657.jpeg 52C7207F-D346-4343-8422-4BD869B691AC.jpeg 9240439B-FC27-46E4-A57D-13C5F86D94F9.jpeg D6969259-DF87-431D-AC96-5DB0737BDAC5.jpeg 89FF07CC-53C8-454A-9151-E7C7F752ACC1.jpeg BADF2949-1510-4C50-B1FB-3A0B1CEA91BD.jpeg
 

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that loose hose use to go to the charcoal canister the hose should have a plug on the end if not in use. I believe that hose use to go to the stock throttle body as part of the smog control unit. You can also remove the charcoal canister if you are no longer going to be using it.

Check the 34mm throttle body to make sure the air screw is brass and not the OEM stock screw "black plastic screw" if the screw is black replace it with a brass screw because that is problem number one for Koso 34mm throttle body.

The other thing is the 02 sensor on the head should be removed and the hole plugged up when you get the WB02 since the 02 sensor on the exhaust pipe will take care of any adjustment.

Good luck
 

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Discussion Starter #18
that loose hose use to go to the charcoal canister the hose should have a plug on the end if not in use. I believe that hose use to go to the stock throttle body as part of the smog control unit. You can also remove the charcoal canister if you are no longer going to be using it.

Check the 34mm throttle body to make sure the air screw is brass and not the OEM stock screw "black plastic screw" if the screw is black replace it with a brass screw because that is problem number one for Koso 34mm throttle body.

The other thing is the 02 sensor on the head should be removed and the hole plugged up when you get the WB02 since the 02 sensor on the exhaust pipe will take care of any adjustment.

Good luck
What is the reasoning behind the plastic screw not working with the new throttle body?
 

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Something about it backing out on its own,,, so its suggested to replace with brass one.

 

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Discussion Starter #20 (Edited)
Something about it backing out on its own,,, so its suggested to replace with brass one.

Ah. I see. I’ll deal with that problem down the road. Would like the bike working correctly first.

I went ahead and ordered new piston rings and spark plugs. Plan on pulling the head off and checking it out when they get here. Talked to the tech at Koso and he said the smoking exhaust and black wet spark plug was probably piston rings. Once that’s done, I’ll add the WB2 and see if the sputtering and bogging down issue is resolved.
Thanks for all the help so far from everyone, though.

Edit: I noticed when taking the air box off, the right side air hose is only really shoved into the air box with nothing to seal it like the original hose. Could this be causing some of the problem such as stuttering? See pic: 360C1A15-3923-4375-B98D-DE547C0AEB46.jpeg
 
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