88 gl1500 off idle stumble


Information and questions on GL1500 Goldwings (1988-2000)
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virgilmobile
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88 gl1500 off idle stumble

Postby virgilmobile » Wed Jul 04, 2012 4:10 pm



Yup,here I am again with this.
My 88 used to stumble and then jump so bad I hated to drive it.
I have modified the accelerator pump and replaced the $50 diaphragm.
Well it's much better...almost 100%....One time in 1st gear and in a intersection,it burped,just a little mind you,but enough to break traction and slide the ass end of the bike around.
THAT"S IT....I had to finally figure out what was wrong.

Here's what I did and the question....
I added a piece of SS rod bent under a screw and extended it into the carb.The end of the rod holds the slide open about 6-8mm(about 3/16")....I put the air cleaner back on and drove it for 2 days.
So far there hasn't been a hint of hesitation.
Now the question...I wonder,did I just overcome the 88-89 design flaw...Air flow,vacuum,mixture,etc...
Or is it possible the rubber diaphragms(25 years old) are stiff and not allowing the slide to pop open on that first throttle demand?
When I cleaned up the carbs,I did check them,They were clean,no holes or cracking and seemed to work fine.I also know that the slides don't usually move until there is a significant load on the engine(air flow)..
So I'm thinking because it absolutely pulls great,the slides are functioning normal ..
Here's the video...




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zamboni920
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Location: Stavanger, Norway
Motorcycle: 1996 GL1500 SE with Hannigan 2+2 sidecar

Re: 88 gl1500 off idle stumble

Postby zamboni920 » Wed Jul 04, 2012 9:16 pm

Looking at my spare carbs, the slide itself never closes the throttle bore completely. Assuming you mean the needle, I notice the needle is spring loaded as it sits in the end of the slide. The spring have the ability to move the needle about 1/8 inch. Could this part be stuck? Also, on the carburator side of the diaphragm, the slide has a grove that fits onto a neck in the carb. This grove contains a "washer" of sorts. If this washer is missing, the slide(and thereby the needle) will drop too far into carb. Only about 1/16 inch, but might be enough. If it seems lifting the slide/needle off a little helps, you might be able to add "washers" to desired "lift" .
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virgilmobile
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Joined: Sun Sep 19, 2010 5:39 pm
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Motorcycle: 1988 GL1500 I
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81 GL1100
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83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: 88 gl1500 off idle stumble

Postby virgilmobile » Wed Jul 04, 2012 10:43 pm

Everything you show is exactly like mine and my slides also don't completely close off the throat.
I used the washer on the needle on by 1200 to fix a lean mixture at 2000 rpm range.A small needle raise at a idle had no effect.
I guess(fortunately)my carbs have never been removed by anybody before me.
It is original OEM,not even a factory mod was done to it.
What I'm guessing is that at the moment I crack the throttle,there isn't enough air flow.
I now have a good accelerator pump squirt,so there's plenty of fuel.

I simply lifted the slide from it's normal "at rest" position a little higher(3/16") for just a bit more air on the throttle crack.
I didn't need more fuel(lifting the needle) I need more instant air.

With all that said,I've read about mods to the Harley carbs where they drill out the vacuum port in the slide to improve throttle response.
I'm not sure that would help here,it has good response,the slides do jump up,It's just lacking air at the crack of the throttle.

This seems to be inherent in the 88-89 model and was fixed in the later years.
I'm hoping this is a design flaw I've stumbled on.It wouldn't be the first one I've seen on this model.

I'm still muddling through the data I'm compiling to see if there is a better mod than 2 pieces of wire stuck down the throat of the carbs.I know its ghetto,Hey...it was just a test. :geek:
So far,with a fifty miles of in town stop and go driving,it hasn't burped once. :)

I've been working on this one step at a time to finally be able to put to rest "what to do" about the off idle stumble problem so many riders just live with applying tested changes.
Obviously it's not just one thing going on here.

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zamboni920
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Re: 88 gl1500 off idle stumble

Postby zamboni920 » Thu Jul 05, 2012 3:11 pm

Soooo....maybe adding some washers to the neck of the slide itself would do it. That would give you a positive, permanent lift to the slide. An O-ring of suitable size and material would perhaps work. Another possible issue is you do not get enough early vacuum to properly move the slide at that exact critical point. For this, I think maybe shorten the long spring wich seats the slide closed. Basically lighten the return pressure on the slide.
If the carbs were a bit (a lot) easier to get to, I would enjoy doing some experimenting myself. If nothing else, just to see how much modification I could get away with :twisted: .

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virgilmobile
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84 GL 1200 I

Re: 88 gl1500 off idle stumble

Postby virgilmobile » Thu Jul 05, 2012 3:46 pm

Thats what I'm leaning to do.Add a "O" ring.
I'm concerned about it not running at a load (5k rpm) without the air cleaner and cover on.
There are so many variables.Are the rubbers lost their resiliency ???? and the air cleaner and cover covering up the problem???
Does it normally run badly without the air cleaner on????Mine spits and sputters horrible without it on.

amsoilguy
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Re: 88 gl1500 off idle stumble

Postby amsoilguy » Thu Jul 05, 2012 6:21 pm

I recently purchased an '88 1500 and I'm totally new to goldwings so please forgive my ignorance. Mine has the same stumble and I have zero experience working on these. I don't suppose you have pic of your modification?

I have read that Honda had a recall of some type for this problem and have no idea if mine was done. Is that true?

Thanks.

EDIT: Going back over previous shop receipts from the PO, the last time it was worked on (06/10) he mentioned this problem and the shop said: "Adjusted carbs to get running better. Should run better after putting some miles on it." No specifics on what they adjusted.

The PO only put on about 800 miles on it since then. Should I wait to do anything until I put some more miles on it?
Allan

'88 GL1500

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virgilmobile
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Joined: Sun Sep 19, 2010 5:39 pm
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Motorcycle: 1988 GL1500 I
Previously owned
78 GL1000
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83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: 88 gl1500 off idle stumble

Postby virgilmobile » Thu Jul 05, 2012 6:33 pm

There was a recall. It entailed hose routing, replacing the low speed jets,ECM and ccm modules, both are hard to find and expensive.I'm convinced it's a production flaw in the carbs.I've got mine back out and I will try to compile all the mods I've done and what each had a effect on the bike.
So far it's been vacuum hoses,increased jet size,lowered the float level modified the accelerator pump and now I'm mucking with the slide rest position and response.

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zamboni920
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Re: 88 gl1500 off idle stumble

Postby zamboni920 » Thu Jul 05, 2012 9:14 pm

Did you only increase size of the main jet?

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virgilmobile
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Joined: Sun Sep 19, 2010 5:39 pm
Location: Denham Springs,La.
Motorcycle: 1988 GL1500 I
Previously owned
78 GL1000
81 GL1100
82 GL1100 I
83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: 88 gl1500 off idle stumble

Postby virgilmobile » Thu Jul 05, 2012 10:28 pm

No,Just the idle jet.it was a #55.I bored it out to a #60.
I'll be running it round town Friday afternoon for at least 3-4 hours under all road conditions to see if it performs continuously good.
My last mod was to install a o ring as a spacer on the slide.If it holds up ok I'll post all the stuff I've done with pictures.

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zamboni920
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Re: 88 gl1500 off idle stumble

Postby zamboni920 » Fri Jul 06, 2012 3:38 pm

Very interested to see the results of this last mod, and also a summary of your efforts.
To my understanding.....and please correct me if I am wrong..... the slow jet (wich is the one you call idle jet) controls throttle response from approximately 1/8 to 1/4 throttle, the slide & needle does the job from 1/4 to 7/8 throttle, the main jet does the rest from 7/8 to wide open . The real idle jet, wich in the case of our Keihin CV carbs actually are the idle mixture screw, controls the carb from idle to 1/8 throttle.
Perhaps you need to play with idle mixture screws?
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virgilmobile
Posts: 7663
Joined: Sun Sep 19, 2010 5:39 pm
Location: Denham Springs,La.
Motorcycle: 1988 GL1500 I
Previously owned
78 GL1000
81 GL1100
82 GL1100 I
83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: 88 gl1500 off idle stumble

Postby virgilmobile » Fri Jul 06, 2012 6:40 pm

Yes,you are more detailed than I was and changing the jet was to provide just a touch more fuel from the idle to 1000 rpm level
This was seen in in the slow jets(the holes at the throttle plate) as I adjusted the needle for proper fuel mix at a idle.
The odd part was,after I changed the jet,I also had to change the float level.it was now overloading just a bit too much.I ended up setting the floats from 8mm to 10mm to lean it out.
I saw this rich condition from 1000 rpm to 1800 rpm
I am debating now that in my case(I should of used the choke) that the mix was ok for my engine and just changing the slide was the best fix,after the pump obviously.
Sooooo a good analysis is always needed first.
I'm working up test methods for each step




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