Hesitation, stumble off idle


Information and questions on GL1200 Goldwings (1984-1987)
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nagger007
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Motorcycle: 1985 GL1200L Limited Edition

Hesitation, stumble off idle

Postby nagger007 » Sun Jul 08, 2012 2:14 pm



1985 Goldwing LTD has a hesitation, stumble coming off idle or running along at light throttle. Bike starts and idles fine, works great at full throtle but if you slow down behind a slow moving vehicle, it doesn't want to pick it up again smoothly unless you really crack the throttle. Also I noticed if you hit a bump it will stumble, but not all the time. Any ideas on this. Also no codes on the computer.



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Re: Hesitation, stumble off idle

Postby bustedwing » Sun Jul 08, 2012 9:20 pm

Had the same problem with an 85 that had sat for a few years and the carbs had a lot of old dirty gas in them, used some Sea Foam for several tanks of gas and made a worid of a difference. If that don't work you may need to get the carbs rebuilt.You could also check the vacuum lines, that old of a bike the rubber lines are getting brittle and a small crack will do the same thing.Good luck, ride safe. Bud.
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nagger007
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Re: Hesitation, stumble off idle

Postby nagger007 » Sun Jul 08, 2012 9:44 pm

Would Sea Foam work on a fuel injected bike? About 4 weeks ago I drove a 450km trip and the bike worked awesome. I bought the bike a year ago not running, after replacing the crankshaft angle sensor we went for a long drive. After about an hour and a half in slow traffic the bike felt like it was trying to stop. I put a little distance between the bikes ahead of me then I wound it out on the throttle and the bike worked great from then on til today. The bike doesn't skip it just stumbles like it is getting loaded up and straightens out for a little when I really crank on it. I was told it had new plugs just before I bought it because he could not get it going.

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WA9FWT
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Re: Hesitation, stumble off idle

Postby WA9FWT » Mon Jul 09, 2012 2:50 pm

nagger007 wrote:Would Sea Foam work on a fuel injected bike? About 4 weeks ago I drove a 450km trip and the bike worked awesome. I bought the bike a year ago not running, after replacing the crankshaft angle sensor we went for a long drive. After about an hour and a half in slow traffic the bike felt like it was trying to stop. I put a little distance between the bikes ahead of me then I wound it out on the throttle and the bike worked great from then on til today. The bike doesn't skip it just stumbles like it is getting loaded up and straightens out for a little when I really crank on it. I was told it had new plugs just before I bought it because he could not get it going.


Yes, to the answer of using Sea-Foam. When was the last time the fuel filter was replaced. First I thought it was a lack of fuel,but when you said it seems to load up ? Maybe just some crap in those carbs yet.Run a few tanks of Sea-Foam and see if that helps .I would also check your fuel pump pressure.

WA9FWT Phil

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Re: Hesitation, stumble off idle

Postby virgilmobile » Mon Jul 09, 2012 3:52 pm

Uh.....Fuel injected carbs????
Ok....just fuel injected.....Hit a bump and it stumbles....
Now the fog has cleared up just a bit.
first....loading up....Remember this thing is computer controlled.Mainly by the throttle position sensor.
It gets a reference voltage of precisely 5 volts from the ECU.Then it's divided down to a lower voltage that is sent back to the ECU which both can be measured at the ECU plug.
The other sensors that come into play are the Pb sensor...there's 2 of them and they have a vacuum line hooked to them.Check the lines.
Obviously I'm most interested in the intermittent thing going on.
I'd really be looking very close at all the electrical plugs for corrosion.
Many times,just removing a plug,cleaning with contact cleaner and putting it back on and off a few times will scuff the contacts clean again.

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WA9FWT
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Re: Hesitation, stumble off idle

Postby WA9FWT » Mon Jul 09, 2012 6:37 pm

virgilmobile wrote:Uh.....Fuel injected carbs????
Ok....just fuel injected.....Hit a bump and it stumbles....
Now the fog has cleared up just a bit.
first....loading up....Remember this thing is computer controlled.Mainly by the throttle position sensor.
It gets a reference voltage of precisely 5 volts from the ECU.Then it's divided down to a lower voltage that is sent back to the ECU which both can be measured at the ECU plug.
The other sensors that come into play are the Pb sensor...there's 2 of them and they have a vacuum line hooked to them.Check the lines.
Obviously I'm most interested in the intermittent thing going on.
I'd really be looking very close at all the electrical plugs for corrosion.
Many times,just removing a plug,cleaning with contact cleaner and putting it back on and off a few times will scuff the contacts clean again.

I missed the boat on this one sorry!! Egg is all over my face.Old man was sleeping......

WA9FWT Phil

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Re: Hesitation, stumble off idle

Postby nagger007 » Tue Jul 17, 2012 8:06 pm

I've tried the Sea-Foam but had a lot of trouble with it. The last time I had it on the road it stalled five times (just shuts down). It would restart if I opened up the throttle. I had to have the bike trailered home. Now I've drained out all the gas with Sea-Foam in it and put in fresh gas. I'm told that fuel injection and related parts for this bike are no longer available. At this point the bike will start and run but will not idle. Also at times it will seem like it is skipping and running very rich and times it will run almost perfect but will not idle. I was first thinking maybe a vacuum leak but can't find any. What problems will the throttle position sensor cause even though there are no codes at the computer? Will a faulty fuel pressure regulator cause this problem. I don't know what the fuel pressure is, I have no way to check it. And how can I fool the temperature sensor to say I have a warm engine and is it the one with the green plug? It seems like some stupid little thing will fix this bike but I can't find it.

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Re: Hesitation, stumble off idle

Postby Ghostrider52005 » Tue Jul 17, 2012 10:05 pm

If sea foam caused you all that trouble I would seriously be looking at the fuel filter. Sea foam will move water, and gunk out of the system but only to a point. If you have a fuel filter thats got a lot of water in it sea foam could cause you stall i suppose.
If your pulling any air into the fuel system thru a pin hole in a fuel line or a fitting it wont run right either.
The fast idle is pretty easy to tell if its working. when you start up in the am unless its awfully hot outside the bike should fast idle until it warms up a little then the rpms drop back down. If its not doing that its probably not working but ive not seen that cause all the problems your having.

If its some sensor tps or something electrical out of specs it should be tossing a code at the computer of some kind.
We have a tendency to blame the fuel injection right off on the LTD when a lot of times it something else like a weak coil or bad wires or plugs etc etc. It could be your FI but could also be something totally unrelated to the FI
Last edited by Ghostrider52005 on Tue Jul 17, 2012 10:13 pm, edited 1 time in total.

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virgilmobile
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Re: Hesitation, stumble off idle

Postby virgilmobile » Tue Jul 17, 2012 10:12 pm

You have a lot of questions there and it will take a bunch to go through it all.
Might I first suggest downloading the closest manual for your bike and reading through the fuel system section.
Also,here's a post dealing with a ECU.....viewtopic.php?f=5&t=12158

It was never positively identified as a defective ECU,only that it didn't work until left unplugged for a day.
It possibly "reset" or a corroded connection was finally made better by unplugging and plugging it it a few times.
In your first post you mentioned that "if you hit a bump it will stumble"...This leads me to believe your problem is electrical connections or a bad throttle position sensor.There is a "by the book" test for it.
Also,the throttle position sensor receives 5 volts from the ECU,one terminal sends a voltage back to the ECU.
The voltage is proportional to the throttle setting and should be very stable.This is a very small voltage,something like 1 volt to 4 volts so any bad connection can really upset the ECU.
It's the primary signal that controls how long the injectors remain open.A false(intermittent)voltage will mess up the fuel delivery duration and can make it run rich or lean.

This should be your starting point.
Personally I would get some contact cleaner,unplug every connection related to the ECU,spray it and connect it back on and off a few times to rub clean the connections.Then try it again.

I'm going by the fact that it used to run pretty good...just had a idle problem and was intermittent.
Obviously there may be multiple problems,(fuel filter,pump,sensors,etc)but let's get it back to where it was to start with.

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Re: Hesitation, stumble off idle

Postby Ghostrider52005 » Tue Jul 17, 2012 10:32 pm

Just a thought but is the bike coverted to the external alternator??? If it is and the alternator is touching the TPS even a tiny bit it will cause all kinds of wierd stuff like your talking about.

nagger007
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Re: Hesitation, stumble off idle

Postby nagger007 » Wed Jul 18, 2012 5:18 am

This bike has never been converted to an external alternator, and I've noticed it has never had a fast idle when cold. Now I've only had the bike a year and not very familiar with fuel injection not even with cars as I work in a General Motors dealership as a technician. Since I took the Sea-Foam out it does run better, almost the same as before anything happened only that it won't idle and has a slight hesitation and at times seems to mix up and smoke. It has really good fire on all cylinders, blue spark with a plug tester. Right now this idle thing really bothers me.

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Re: Hesitation, stumble off idle

Postby virgilmobile » Wed Jul 18, 2012 8:34 am

Are you able to download a suable manual to guide you to the test points?

The idle system.....
There are a few things that must be exactly right for it to idle properly.
You can eliminate the fuel filter and pump as the bike does run out ok.
It won't be related to the compression or spark for the same reason.
What will affect the idle....

Fuel rail pressure...It's a bit lower at a idle than at running speed,I think that its vacuum that controls the pressure regulator,So test the fuel pressure.Too high a pressure will run the bike rich,too low and it leans out.Either will upset the idle.Be certain it's within the specs.

The throttle position sensor.Yes it can be bad or mis adjusted and the ECU not show a code.You need to get a DVM and look at the book for the exact voltages it should have.Even off by 1 volt will change the injector duration.

The output voltage of both Pb sensors,there are two of them.They monitor the vacuum of each bank to keep the engine balanced.Kinda like a sync sensor.Measure them.
Obviously they are vacuum operated and if they have the right output voltage at a specific vacuum test,the vacuum lines ase suspect.

Run a few preliminary tests on the major systems to it narrow down.




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