[Strokd_GE]

Since we don't have a "Troubleshooting" section yet, I'll post here

Last Sunday I pulled the head off my Grom to give it some mild porting and to clean up to combustion chamber, I just smoothed the walls, removed the casting marks and opened up the exhaust a smidge, nothing major

after reinstalling everything I reset the ECU via the red plug under the seat, fire it up, it stumbled idling for a couple seconds and the cel flashed a few times, went away and the idle cleared up.. After idling for about a minute I blipped the throttle and when the rev would reach the bend in the tach (3-4k?) it would hesitate (this cleared up after riding) and continue revving a bit sluggishly, I rode to work the next day an it was way sluggish and wouldn't rev over 8k, I assumed the cam timing was off and that night when I got home I checked it, it was 1 tooth advanced which I corrected

Now with the cam reclocked I reset the ECU again, fired it up, everything was fine, stumbled in the same 3-4k ranged but cleared up with light throttle riding around the neighborhood, power was back on point so after a few laps to warm up I ripped it wot.. 3.. 4.. 5.. (Nice and smooth) 6.. 7.. 7.5.. (stuttering bog) 8k and struggling to rev beyond it in any gear

Back at the house I started checking connections, everything was good, so I thought maybe the ECU was struggling to adjust to the port at high rpms, so I take the stock intake pipe and instal it and go for another ride, still breaking up at 7.5-8k.. I take a pair of needle nose vice grips and pinch the hose down, another lap and it sputtered and bogged the whole rpm range.. Strange? so I made a final lap open tb and it was the best run out of them all, pulled great down low, mid and revved out to about 8-8.5 before developing the same bog

Heres where I'm confused, it seems as though the high rpm bog is from too much fuel or the exhaust gas is not getting out fast enough.. Maybe due to the porting but not so sure since I barely took any metal out

Any ideas as to what may be going on? I'm tempted to pull the head apart again and check for anything weird or maybe installed wrong, I also thought while typing this that maybe since the o2 sensor is now more exposed in the exhaust port due to the porting, I wonder if it's readings are off and that maybe I should shim it out to adjust what it's "seeing"

I'm kind of stuck right now with ideas other than just buying a new cylinder head and taking it as a learning experience haha but thought I would post up to see if anyone had ideas to try

 

[Strokd_GE]

Taken from the EJK thread an PitBiker

Could explain the bog

The reason that the fueling starts to change around 7,000 RPM is because the ECU is switching from a closed loop fuel map to an open loop fuel map.

 

[The green]

How long did you drive after reset? It takes mine about 25km..


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[Strokd_GE]

How long did you drive after reset? It takes mine about 25km..

Not nearly that far, maybe 5km at most

my initial thought was that it was leaning out so I didn't want to ride too far and the engine go pop

 

[CiscoSanJose]

Since we don't have a "Troubleshooting" section yet, I'll post here

Last Sunday I pulled the head off my Grom to give it some mild porting and to clean up to combustion chamber, I just smoothed the walls, removed the casting marks and opened up the exhaust a smidge, nothing major

after reinstalling everything I reset the ECU via the red plug under the seat, fire it up, it stumbled idling for a couple seconds and the cel flashed a few times, went away and the idle cleared up.. After idling for about a minute I blipped the throttle and when the rev would reach the bend in the tach (3-4k?) it would hesitate (this cleared up after riding) and continue revving a bit sluggishly, I rode to work the next day an it was way sluggish and wouldn't rev over 8k, I assumed the cam timing was off and that night when I got home I checked it, it was 1 tooth advanced which I corrected

Now with the cam reclocked I reset the ECU again, fired it up, everything was fine, stumbled in the same 3-4k ranged but cleared up with light throttle riding around the neighborhood, power was back on point so after a few laps to warm up I ripped it wot.. 3.. 4.. 5.. (Nice and smooth) 6.. 7.. 7.5.. (stuttering bog) 8k and struggling to rev beyond it in any gear

Back at the house I started checking connections, everything was good, so I thought maybe the ECU was struggling to adjust to the port at high rpms, so I take the stock intake pipe and instal it and go for another ride, still breaking up at 7.5-8k.. I take a pair of needle nose vice grips and pinch the hose down, another lap and it sputtered and bogged the whole rpm range.. Strange? so I made a final lap open tb and it was the best run out of them all, pulled great down low, mid and revved out to about 8-8.5 before developing the same bog

Heres where I'm confused, it seems as though the high rpm bog is from too much fuel or the exhaust gas is not getting out fast enough.. Maybe due to the porting but not so sure since I barely took any metal out

Any ideas as to what may be going on? I'm tempted to pull the head apart again and check for anything weird or maybe installed wrong, I also thought while typing this that maybe since the o2 sensor is now more exposed in the exhaust port due to the porting, I wonder if it's readings are off and that maybe I should shim it out to adjust what it's "seeing"

I'm kind of stuck right now with ideas other than just buying a new cylinder head and taking it as a learning experience haha but thought I would post up to see if anyone had ideas to try

PM BrianS for some info since he has been working on the 170cc kit and head mods on the Grom and he might have come across the same problem you are having.

Usually tell tail sign of any engine bogging down or fuel problem could be checked by looking at the spark plug color after a short/long ride. Smell of raw fuel when Grom is idling.

Almost sounds like FI circuit problem to me or ECU re-cal problem.

My Hayabusa did the same thing like your Grom is doing and I could smell raw gas when at idle and when I open the bike up it would break down and not go above a certain rpm and it ran great at idle and with no load. My problem ended up being the fuel filter inside the electronic fuel pump needed cleaning and was part of the problem and the second problem was the FI injectors was fouling up due some connection to the ECU. Unplug and reconnected everything and cleaned out the fuel filter and the ran some FI cleaner and it solved my problem.

Can't see how porting can cause the problem you are having, I can see the timing being off could cause the problem.

Good luck.

 

[wondermuscle]

Make sure the 02 sensor is clean and didn't get any accidental oil, goop or debris during the install. It doesn't sound like you removed enough material from the head to make such major improvements in flow. I wouldn't expect fuel issues to the degree you are seeing.

 

[BiG Chris]

That is strange when I installed my BBK I ported the head a good deal and put it all back together with the turbo on it and it didnt have any issues like your having, there has to be something causing the problem did you take the valves out of the head?

 

[Strokd_GE]

That is strange when I installed my BBK I ported the head a good deal and put it all back together with the turbo on it and it didnt have any issues like your having, there has to be something causing the problem did you take the valves out of the head?

yeah head was fully disassembled, valves were still in spec after lapping and reassembly

 

[ShapeShifter]

Maybe take the cam out and see if it has grooves in it? Don't know why it would if the timing was only off one tooth but.....

 

[Strokd_GE]

Maybe take the cam out and see if it has grooves in it? Don't know why it would if the timing was only off one tooth but.....

I may pull the head tonight or tomorrow, another thought was that it may have slightly bent a valve when it was out of timing

 

[BiG Chris]

if it was off by one tooth on the cam its shouldn't have bent a valve and if it did have a bent valve it shouldn't start.

 

[RaZed1]

Vacuum leak from the manifold/TB/ash can port? Would make it go lean and bog.

 

[Strokd_GE]

Alright guys, so I finally put a new oem cylinder head on last night, swapped over all the valve train from the ported head to the new one.. Reset the ECU via the red port, same crap as before

Has anyone when resetting the ECU via the red port ever forgotten to remove the jumper before starting the bike? I'm pretty sure I did this after installing the ported head the first time but I also feel like I had done it before that and nothing came of it

for those with a work manual, does it warn to not start the bike whenever it is jumped?

 

[Snakeibf]

I don't think that should be a problem, just do the ECU reset again if you forgot to pull it out. If you have any stored codes in the system the ECU reset wont work. Clear any codes first. The MIL light will flash rapidly then let the throttle off for 3seconds then pull the jumper and it should be fine. I did some head work on mine and never had issues and I've probably had my head off 15 times during all my testing. The ECU will also adjust after 20 or so miles as well. Hopefully you get it sorted out.

Maybe there is something on my site that could help. I added some stuff recently.

Www.inveniamperformance.com

Good luck

Sent from my iPad using HondaGrom.net

 

[Strokd_GE]

Thanks snake

I just came back to post that I'm almost certain i do have a stored code, last night when attempting to reset it the mil would cut off almost as fast as it came on and would flash, I'm leaving work now so I'll clear the codes when I get home

 

[BiG Chris]

let is know what happens

 

[Strokd_GE]

Had codes 8 and 9

8: TPS sensor circuit low voltage
9: IAT sensor circuit low voltage

iat is probably from me starting it without it hooked up, no idea why the tps would be wonky

I'm try to find how to read the codes now *snake explains in the link he provided*

 

[Strokd_GE]

Well now I feel like a fool lol

I cleared the codes from the ECU and then reset it.. Runs like a dream! Thanks again Snake for your link and explaining how to clear the codes

i guess now that I have a spare head I'll send the ported one to be shaved

 

[ShapeShifter]

You're no fool.

We are laying the foundation for the next 50 years of Honda mini bikes.

 

[Grom'n-BR]

^ very true. The grom is new. We are the pioneers of modification on this bike.
Trial and error more often then not