Diagnosing Miss/ Stumble at Idle


Information and questions on GL1100 Goldwings (1980-1983)
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triketrash
Posts: 144
Joined: Wed Dec 04, 2013 4:36 pm
Location: Shelton, WA
Motorcycle: 1981 GL1100 Interstate

Diagnosing Miss/ Stumble at Idle

Postby triketrash » Thu Feb 27, 2014 1:03 pm



Just got through a fork job on my GL1100. Rode it about 60 miles yesterday. I had no trouble until I did this fork job. The thing that comes to mind is that I had the choke line off the handlebars to access the top of the forks. I did put some pressure on it. I'm wondering if the choke is not fully closing now. Do you think a little choke at idle on a warm engine could cause the stumble/ miss that I'm talking about? The bike runs fine at idle when first started with full choke. It has no miss/ hesitation with acceleration or cruise. It's just once the bike warms up and is at idle that I have the problem. The other thing is that I'm noticing the idle rpms are higher than they used to be. You think this points to choke, or maybe more likely vacuum leak? If the latter, is there a schematic I can look at that highlights the vacuum system? Thanks, Vince



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RoadRogue
Posts: 1913
Joined: Sun Jun 06, 2010 10:51 pm
Location: Castlegar BC, Canada
Motorcycle: 1997 1500SE

Re: Diagnosing Miss/ Stumble at Idle

Postby RoadRogue » Thu Feb 27, 2014 4:09 pm

It sure sounds to me like you have the choke still on a little. Pull the air filter and use a small mirror to look into the carbs down the intake plenum.you might just see the problem. Take a look at where the choke cable attaches to the carb linkage, did it slip from its anchor? 8-)
Ride safe, Todd
Over night campers welcome

User avatar
triketrash
Posts: 144
Joined: Wed Dec 04, 2013 4:36 pm
Location: Shelton, WA
Motorcycle: 1981 GL1100 Interstate

Re: Diagnosing Miss/ Stumble at Idle

Postby triketrash » Thu Feb 27, 2014 4:50 pm

Well I have some more info on this. At lunch I took the bike for a short run to warm it up and, again, there's a pronounced miss at idle. You feel it as you roll the throttle on to some extent, but it's not really noticeable in acceleration or cruise setting. I then checked the compressions, and they are solid 155-160 all the way around, so that valve that I recently replaced is holding steady- phew! I then took a timing light to each of the spark plug leads. It's the old dinosaur kind where you have to remove the plug boot, put this spring thingy over the plug, and the other end of the thingy into the timing light boot. I couldn't see a noticeable flicker in the light on any of the cylinders when the miss did its thing, so I'm thinking the electrical out to the end of the wires is ok. But.... on plug number 1 ( I think that's right- right forward cylinder) when I went to use the gun, there was no light. It turned out the springy thing had fallen off the spark plug. Now- here's the interesting part- at this point the bike is running on only 3 cylinders because that spring is off the plug- the bike doesn't sound too bad AND there's no miss. As soon as I reconnected the timing light properly, the miss showed up again. What does that tell you- maybe a bad plug on that cylinder? At the very least- I'm definitely leaning toward something electrical at this point. I did check that choke system and all looks ok there.

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RoadRogue
Posts: 1913
Joined: Sun Jun 06, 2010 10:51 pm
Location: Castlegar BC, Canada
Motorcycle: 1997 1500SE

Re: Diagnosing Miss/ Stumble at Idle

Postby RoadRogue » Thu Feb 27, 2014 5:32 pm

The spark plug caps are just screwed into the wires. Remove #1 and cut about 1/4" off of the wire to get to " fresh meat" . The wires are stranded copper and sometimes they get corroded causing resistance to increase. Actually it wouldnt hurt to do all four wires, you can do the same thing at the coil end or you can just replace the wires all together . You can get bulk wires at most auto part stores. 8-)
Ride safe, Todd
Over night campers welcome

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RoadRogue
Posts: 1913
Joined: Sun Jun 06, 2010 10:51 pm
Location: Castlegar BC, Canada
Motorcycle: 1997 1500SE

Re: Diagnosing Miss/ Stumble at Idle

Postby RoadRogue » Thu Feb 27, 2014 9:02 pm

Also the spark plug caps can be unscrewed. There is a resistor in there for radio noise suppression. It show read 5K ohms, while you have it apart look for corrosion in there too. Try moving number one plug to another cylinder and see if the issue follows it. There areonly so many places the miss can be coming from, its just a matter of chasing down the right one 8-)
Ride safe, Todd
Over night campers welcome

User avatar
triketrash
Posts: 144
Joined: Wed Dec 04, 2013 4:36 pm
Location: Shelton, WA
Motorcycle: 1981 GL1100 Interstate

Re: Diagnosing Miss/ Stumble at Idle

Postby triketrash » Fri Feb 28, 2014 12:24 am

Well I am thrilled to pass on that the mystery of the recently appearing miss at idle has been solved. After testing the leads at lunch and believing them to be sound I thought I should rule out the spark plugs, even though I have NEVER personally had a plug go bad on me. I can't tell you the number of times I've changed plugs, and usually just as a maintenance item, but never have I put new plugs in and seen a big difference in the way the thing runs. So, given this history I wasn't even really keen on buying a new set, even though it's only a few bucks. So, I pulled the crusty old corroded plugs out of my parts bike. As I removed the plug caps, a big clump of straw and moss fell out of the hole! They didn't look great, but I thought at least I could see if there was any change in the way the bike idled. Switched them out, and the bike ran like a top. Got it warmed up, and NO MISS. I rode home from the hangar- back to the way it was running a few weeks ago. SO never say never- plugs do go bad I guess. And these were fairly new plugs that looked pretty good as far as color and so on.

I was so worried I was going to fine low compression on that cylinder that I changed a valve out on a few weeks back. Unreal.

On the bad side, I inspected my newly rebuilt forks now that I have a few miles on them and....... the same fork that was leaking before the rebuild is leaking again. Oh well, no biggy- I can deal with that. Pull it apart and try again.

thanks for your help guys, especially RoadRogue:-)

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RoadRogue
Posts: 1913
Joined: Sun Jun 06, 2010 10:51 pm
Location: Castlegar BC, Canada
Motorcycle: 1997 1500SE

Re: Diagnosing Miss/ Stumble at Idle

Postby RoadRogue » Fri Feb 28, 2014 1:52 am

And sometimes its the easiest and cheap items that fix the issues we have. Glad to hear its purring again. Now back to what started this madness. Good luck! 8-)


Ride safe, Todd
Over night campers welcome


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