Stumble Hyphothesis

[zzcop8]

This is just a Wild A## Guess on my part but here goes. Now before I start I have a 2012 and have had no stumble or brake problems. I was wondering that those folks that have had the dreaded Stumble ,could this have been caused by something other than the engine. Have you just used your brakes then start to accelerate when you got the stumble. What I am trying to say is could your rear brake be hanging up (as in the Recall) which in turn would pull your engine down simulating a stumble. As stated at the beginning this is just a guess,as to my knowledge they have not found anything definitive in the ECU.

[Cruiseman]

I don't think so in my case. My stumble usually occurs right after I head out in the morning, when it is cool. It happens about 2 blocks from my home, just about the time the temp gauge hits the first little tick mark on the temp scale.

[cmock]

Ive had the stumble since about new and it is for sure the throttle/fuel supply. However mine is starting to be less frequent in nature. Not sure if it is because of the cooler weather or not. We shall see next year when the temps come back up and see if it starts again. 6300 miles on mine.

[Riverdawg]

Mine is a 2013. In the mornings, at 30mph, I know exactly when the power droop (as I call it) is going to occur within 1/4 to 1/3 mile after leaving the driveway. It feels and sounds just like you pulled a plug wire for about 10-15 seconds. Mine is no braking issue, after that distance or time has passed, whichever one it is, it never does it again until you park it for a while. In the afternoon, from work, I take off and accel to 60+ mph, I never feel it.

[Cruiseman]

Sounds exactly like mine.

[RaConnol]

And yet my 2010 never stumbles unless its darn cold outside ie near freezing, but not if I let the bike warm up.
I would be interesting to swap ECU between bike that stumbles and one that does not and see what happens. The only risk might getting your ECU back.

Rick

[zzcop8]

Thanks for the replies. As I stated it was just a WAG and trying to assist those that have the problem and do not know what causes it. Just looking from another point of view.

[Riverdawg]

Hey zzcop8, thanks for any input on this issue. Maybe somebody will figure this out even if it starts with a WAG.

[glarson3]

Hey zzcop8, thanks for any input on this issue. Maybe somebody will figure this out even if it starts with a WAG.

Agreed. Thank you for any thoughts on this. To add, mine does it in neutral or clutch pulled in, and the RPM's drop drastically, and then surge back to normal. It happened today in a parking lot. I checked the temp gauge, and it was not displaying the engine as cold. It's not the brakes with mine, but that's not to say that perhaps some are experiencing an issue with brakes, and might think what we're describing is their issue.

[Tony in AZ]

My 2004 , the 2008 or the 2010 (RIP) never stumbled like this 2013 does. I know when the temp gauge needle starts to rise, the engine will stumble when throttle is added. When I leave work, I am careful as I move out into traffic because of this stumble problem Honda engineers created

[lyle doverspike]

I do not think my 2012 stumble is related to a brake drag issue either. I have reached 59,000 miles and have not ever noticed any brake drag. I get the stumble after the needle reaches the next to lowest mark on the temp gauge. Also when the bike is ridden and temp is normal and parked for 15 to 20 minutes, then started and after a minute or two it stumbles. I am very cautious at those conditions so as not to get caught making a turn when it stumbles. On third set of NGK stock plugs.

[Bike49]

At some point the Wing clears the fuel fume absorption canister by ingesting the contents. The SM describes the plumbing and controlling valve. Not sure when that happens. Might cause rough running if it upsets the A/F mixture. No fumes = might briefly go lean. Fumes = might briefly go rich. Just another WAG.

My '13 F6B has yet to misbehave. I let it warm to the "C" mark and ride off.

Edit: Read the SM and see if it makes sense. Why some bikes and not others? Maybe variability in fuel vapor pressure, ambient temperatures, initial air bypass screw settings (not sure if and when they're critical to running), wonky Idle air control valve, switching from open loop (start) fueling to closed loop cruise (via O2 sensors), faulty engine sensors, and the list goes on.

Oh, and the GL1800B F6B has a different P/N throttle body than the standard GL1800 Wing. Not sure if F6B's have the same % of Stumbling.

[JeffP]

My 2013 F6B has a light stumble when cold but goes away quickly after a few minutes. I'm really not concerned as I usually find a good roll on the throttle clears it up.

[Bike49]

Riders with the stumble if interested in eliminating my first WAG above might try this: Under the right front side of the engine behind the right horn is the black round fuel fume absorption canister. It can be easily viewed behind the front tire. Exiting the right side of the canister is the larger of two hoses, the one of interest is slightly offset from the center. Crimp or plug that hose to prevent flow and see if the stumble continues or stops, but leave it connected to the canister for safety purposes. That hose feeds fuel fumes captured by the carbon canister to the purge control solenoid. Don't mess with the rest of the hoses.

See the Service Manual p. 1-31 and 1-108 for details. I have no idea of what will result, but if the fumes are causing a problem the disconnect may help.

[glarson3]

My 2013 F6B has a light stumble when cold but goes away quickly after a few minutes. I'm really not concerned as I usually find a good roll on the throttle clears it up.

Mine has that stumble too. It is just a little hesitation when holding throttle steady when the bike is cold. I would describe it as a 'modulation' where you change a hundred or so RPM's when holding steady, or a little delay when trying to accelerate. Is that what you are describing? The stumble that bothers me is the one where you lose about 1000 RPM's when trying to keep the bike in the friction zone. The stumble I experience seems to occur right around the 1800-2000 RPM, and it will drop to about 1000, and then go back to where you had it(1800-2000).

[Bike49]

I'm not an expert experienced GL1800 owner. But I have been around engines for a while. If the throttle plates are fixed in one position (not throttle by wire but by older design cable), then the only way for the rpms to markedly vary is by changing the engine's ignition parameters, intake airflow, and the air/fuel ratio to all cylinders. On the Gl1800 there are two possible sources of additional air at fixed throttle settings I can think of...the idle air control valve, and the purge control solenoid that empties the absorption canister at some point when running. The engine control module calls for fuel to the engine based upon input from various sensors and where it thinks it is on the fueling map. Same for ignition timing.

So here's how I look at the problem:
1. Is the purge control valve action causing an upset in the intake airflow and air/fuel ratio under certain conditions? That's why I suggested blocking its intake above and seeing if there's any benefit. Anybody know when it's activated? The SM doesn't discuss its behavior.
2. Is the idle air control valve acting properly? The service manual doesn't describe its normal behavior other than some reference to adjusting base idle speed via air bleed screw adjustment. I assume once the bike warms and settles into normal idle speed it only operates to maintain it, and is closed thereafter under higher load demands. However any ingested oil and combustion byproducts may make it act abnormal/stick. Just a guess but that control concept has been known to cause quitting on some Yamaha's, but that was mainly at closed throttle on deceleration.
3. Sensor defects? Anything that sends an abnormal or intermittent signal to the ECM may cause problems. It could be the sensor or a bad wiring issue. There's lots of them. On other bikes I'm familiar with the throttle position sensor, crank angle sensor, rpm sensor, air temp sensor, and others can and have caused running problems.
4. ECM fuel and ignition programming correct? There's some reference elsewhere to reflashing the control unit for improved performance. If it's a post-'12 programming issue, then why don't all GL1800's have a problem? Some apparently don't, some are borderline, and some definitely do.
5. Spark plugs and ignition coils? NGK plugs have been suggested to help. I replaced my Denso's when the bike was new and haven't experienced the stumbling. Did I prevent a problem? And no I'm not going back in with the factory plugs to find out. There's three ignition coils. One dropping out or providing low voltage to its spark plugs could disable two cylinders.

The best approach in my opinion is to do what you can as an owner and test/replace what's simple. Contact your dealer and have the problem documented (like the early '12 GL1800 GPS problems so Honda becomes part of the solution). File a NHTSA report of defect: https://www-odi.nhtsa.dot.gov/Vehicl...nt/index.xhtml

My thoughts is all. Comment or flame away.

[glarson3]

I'm not an expert experienced GL1800 owner. But I have been around engines for a while. If the throttle plates are fixed in one position (not throttle by wire but by older design cable), then the only way for the rpms to markedly vary is by changing the engine's ignition parameters and the air/fuel ratio to all cylinders. On the Gl1800 there are two possible sources of additional air at fixed throttle settings I can think of...the idle air control valve, and the purge control solenoid that empties the absorption canister at some point when running. The engine control module calls for fuel to the engine based upon input from various sensors and where it thinks it is on the fueling map. Same for ignition timing.

So here's how I look at the problem:
1. Is the purge control valve action causing an upset in the air/fuel ratio under certain conditions? That's why I suggested blocking its intake above and seeing if there's any benefit. Anybody know when it's activated? The SM doesn't discuss its behavior.
2. Is the idle air control valve acting properly? The service manual doesn't describe its normal behavior other than some reference to adjusting base idle speed via air bleed screw adjustment. I assume once the bike warms and settles into normal idle speed it only operates to maintain it, and is closed thereafter under higher load demands. However any ingested oil and combustion byproducts may make it act abnormal/stick. Just a guess but that control concept has been known to cause quitting on some Yamaha's
3. Sensor defects? Anything that sends an abnormal or intermittent signal to the ECM may cause problems. It could be the sensor or a bad wiring issue. There's lots of them. On other bikes I'm familiar with the throttle position sensor, crank angle sensor, rpm sensor, air temp sensor, and others can and have caused running problems.
4. ECM fuel and ignition programming correct? There's some reference elsewhere to reflashing the control unit for improved performance. If it's a post-'12 programming issue, then why don't all GL1800's have a problem? Some apparently don't, some are borderline, and some definitely do.
5. Spark plugs and ignition coils? NGK plugs have been suggested to help. I replaced my Denso's when the bike was new and haven't experienced the stumbling. Did I prevent a problem? No. I'm not going back in with the factory plugs to find out. There's three ignition coils. One dropping out or providing low voltage to its spark plugs could disable two cylinders.

The best approach in my opinion is to do what you can as an owner and test/replace what's simple. Contact your dealer and have the problem documented (like the early '12 GL1800 GPS problems so Honda becomes part of the solution). File a NHTSA report of defect: https://www-odi.nhtsa.dot.gov/Vehicl...nt/index.xhtml

My thoughts is all. Comment or flame away.

Some of that stuff went right over my head, but I got the gist of what you're saying. In my case, the NGK plugs made no difference. I'm suspecting it's one of the sensors, and I've documented it with Honda that I experienced the issue when the bike was under warranty, but they stated they could not duplicate the problem. I've also reported it to the NHTSA. I don't know how much the sensors cost, where they are located on the bike, and I don't experience the problem all the time, so it's a difficult nut to crack. I don't think it's a sticking throttle cable because it goes from ~1800 rpms to 1000, then 1800, 1000, etc. Usually after a few minutes of riding the issue is gone.

I definitely appreciate your wisdom. Thank you for sharing.

[Bike49]

Some of that stuff went right over my head, but I got the gist of what you're saying. In my case, the NGK plugs made no difference. I'm suspecting it's one of the sensors, and I've documented it with Honda that I experienced the issue when the bike was under warranty, but they stated they could not duplicate the problem. I've also reported it to the NHTSA. I don't know how much the sensors cost, where they are located on the bike, and I don't experience the problem all the time, so it's a difficult nut to crack. I don't think it's a sticking throttle cable because it goes from ~1800 rpms to 1000, then 1800, 1000, etc. Usually after a few minutes of riding the issue is gone.

I definitely appreciate your wisdom. Thank you for sharing.

There's nothing technical there, just common sense, and no wisdom beyond experience. If you hold the throttle steady, say in neutral, can you dupe the problem at will? Try to set up the test as you would normally go riding for example. Start up cold then try to dupe the problem when cold, if that's when it occurs, as it warms up, then when warmed up after a stop.

Surely someone with access to a dyno on a troubled bike could create the problem at will if it can't be done while not riding and in neutral.

If the throttle plates in the throttle body don't move when held steady by your grip, then the only way the rpms can vary as described is if air, fuel, or ignition vary for some undetermined reason. When first started cold the bike's rpms will be higher than idle when warm, and can range some as the idle air control valve and whatever settle into a normal idle mode as the engine warms up, mainly after the temp passes the cold mark in my limited experience.

I don't know why this happens so these are just WAG's about what could be the source(s).