88 gl1500 stumble revisited.


Information and questions on GL1500 Goldwings (1988-2000)
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virgilmobile
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Location: Denham Springs,La.
Motorcycle: 1988 GL1500 I
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78 GL1000
81 GL1100
82 GL1100 I
83 GL1100 I
83 GL1100 standard
84 GL 1200 I

88 gl1500 stumble revisited.

Postby virgilmobile » Mon Jul 16, 2012 3:59 pm



zamboni920 wrote:Very interested to see the results of this last mod, and also a summary of your efforts.

A synopsis.
88gl1500..1st gear idling at 900 rpm....open the throttle and it bucks and slams the bike.
above 1200 rpm....smooth.
1st attempt...replace every vacuum hose that was weekend......no effect.
2nd pulled carbs....cleaned and polished everything squeaky cleaned....verified accelerator pump did work(kinda)........no improvement.
3rd....revisited the accelerator pump....not working so well....viewtopic.php?f=6&t=11658.....
plugged up the bypass ports and adjusted the pump lever for instant fuel delivery......Helped a bunch.75% improvement.


4th replaced accelerator pump diaphragm ($50)....a little change..more squirt but still a bit of a stumble.improved to %85
5th experimented with the slide...propped it open 3mm....dramatic change.All stumble gone.Now that I have fuel..I need a bit more air

Things I did that either didn't help or made things worse....
1st....arbitrarily bored the slow jet to a #60.
This increased the slow speed fuel to the point that the needle has to be turned in to 1 3/4 turns and also increased the fuel at the 1500 rpm range.It was now running too rich.
I had to reduce the fuel level in the bowl to compensate for a rich condition.
I changed the float to 10mm.

2nd I experimented on the slide by drilling the air port out 30% larger.It was 0.12"..I enlarged it to 0.14"..
this was a attempt to enhance throttle response.....Well it did.....Now it's just a bit touchy.
It takes very little throttle to bring the bike to 3 grand and I do mean very little.
In 3 days riding I haven't opened the throttle past 1/3 open.
It really isn't needed.Just a crack gets it to 3500 rpm in every gear easily.

3rd.unplugged the temp sensor for the CCM module.Although it changed the idle and when the valves operated(rpm),it had no benefit.

4th I decided not to replace the trigger wheel.I've read that it is suggested that that change may also require changing fuel octane.

currently I can approach a intersection and make the corner at 18 mph(still in 4th)800 rpm,roll the throttle just a little and it will pull right back to the speed limit.I never shifted.

All my problema were solved by improving the accelerator pump and opening the slide just a tad.
Now I have fuel and air at the moment I need it...Just off idle..



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dingdong
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Re: 88 gl1500 stumble revisited.

Postby dingdong » Tue Jul 17, 2012 11:56 am

After all the experimenting and modifications what was the most effective mod? You made so many mods do you think any of them were unnecessary? Might one or the other have solved the problem by itself? Did the o-rings on the slides effect the idle? I will be interested in your fuel mileage after the mods. There are a lot of 88 and 89 owners out there that will be interested in this. I know you will but keep us up to date.

Tom
Tom

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virgilmobile
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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 stumble revisited.

Postby virgilmobile » Tue Jul 17, 2012 12:59 pm

:? Most of the mods had little effect and some were just bad,like changing the slow jet.It actually made the bike run rich in the 1000-1500 rpm range.I had to lower the fuel level to compensate.

:? The mod of increasing the port in the slide .....
I'm on the fence about what effect it actually had.
I don't believe it affected the off idle problem in any way.
The slides operate with air flow and the bike really doesn't have much till the throttle is opened up pretty good.There's no activity with them in the low speed range.

:) Raising the slide a few mm. made no change in the idle.It just provides a bit larger opening for more air to mix with the extra fuel I'm injecting as soon as I crack the throttle.

To the best of my test results,the most beneficial "cure" for the persistent off idle stumble ....................when all the rest of the approved methods fail is.................

Rebuild the accelerator pump,plug the bypass holes and adjust the actuator arm on it to operate the pump at the crack of the throttle.
I set mine for constant pressure on the plunger.I'd call it a minus 0.10"
This provided the fuel for the starved engine.

If that doesn't completely eliminate the problem,then raise the slides.
It appears that newer models have done this by the pictures I saw.

Remove the slides and add a "O" ring to lift the slide about 3mm.
This provided the extra air to mix with the accelerator pump fuel.

I just arbitrarily added a 3mm O ring because that was where my first test was set at.
A smaller amount may also work,but I did not test that theory.It takes way too much time to get them out and back in.
A good guess would be from 1.5mm to 3mm.lift would work fine.

My carbs are original equipment...no factory mods were ever done to them.
If yours carbs have been Re-jetted and a new needle put in,just improving the accelerator pump may be enough.

I'd start there first,it's the easiest to get to,and can be done with the carbs still on the bike.

Finally a warning......I did this on my own...to my own bike... I am a communications analyst not a mechanical engineer and I did no Dyna analysis of the torque curve,before or after.

My end result is a bike unlike anything I've driven before.Ungodly amount of torque right at the crack of the throttle,all the way to red line in every gear.
It will extend the forks at a twitch of the throttle.
Maybe it's suppose to be that way.Dunnow,but I like it.

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virgilmobile
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78 GL1000
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82 GL1100 I
83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: 88 gl1500 stumble revisited.

Postby virgilmobile » Tue Jul 17, 2012 1:02 pm

Oh,one more thing......If you want,I'll try to rig up a video of the final running.Holding my Iphone just doesn't work.
I'll keep track of the MPG but is shouldn't have too much of a change on the open road.It does use a bit more on each twist from the mod to the accelerator but I can live with that trade-off.

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zamboni920
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Re: 88 gl1500 stumble revisited.

Postby zamboni920 » Wed Jul 18, 2012 6:18 pm

I like it. Sounds awesome.
I rebuilt mine, but did no mods....just Randakks rebuild kit and adjust the floats. It now runs great, but not quite like yours I believe. Currently working on my 1200 carbs.

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virgilmobile
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78 GL1000
81 GL1100
82 GL1100 I
83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: 88 gl1500 stumble revisited.

Postby virgilmobile » Wed Jul 18, 2012 6:42 pm

After I did my1200 carbs,I had a flutter from180-2500 rpm.I added a little " choke" and it cleared right up.it was a bit lean.I lifted the slide needle with a washer to clear that problem.
Keep me posted on how it turns out.

mrutah12
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Re: 88 gl1500 stumble revisited.

Postby mrutah12 » Tue Jun 09, 2015 2:46 am

what size drill bit do you use for the diaphragm and which is the one you drill i have to holes on the bottom to choose from rework the the accelerator pump and it works better still have stumble right off idle thank you in advance

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virgilmobile
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Previously owned
78 GL1000
81 GL1100
82 GL1100 I
83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: 88 gl1500 stumble revisited.

Postby virgilmobile » Tue Jun 09, 2015 9:53 am

Are we talking about the gl1500 slide port?The 2 holes in the bottom?

mrutah12
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Re: 88 gl1500 stumble revisited.

Postby mrutah12 » Tue Jun 09, 2015 11:27 am

Yes the slide port the two holes on the bottom :P

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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 stumble revisited.

Postby virgilmobile » Tue Jun 09, 2015 12:02 pm

Ok,now I'm in the same page.I enlarged the hole that is in the front..toward the engine.I did not measure the drill bit size,I just picked the next larger one in the box.It enlarged the hole by 20%.
Be aware...This change did not help the off idle hesitation at all.It just made the slides rise a bit faster as I twisted the throttle.
Better throttle response above 1500rpm.
To the best of my thinking,my off idle hesitation was cured by 2 main things.
Getting the accelerator pump working and adjusting the actuator arm at -0.01" and raising the slides 3mm from there normal position with a "O" ring.
A good sync and idle down adjustment are also needed.

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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 stumble revisited.

Postby virgilmobile » Tue Jun 09, 2015 12:13 pm

One more thing.Keep in mind that these mods were done to a original equipment not factory upgraded 1988 carb.The mods were done instead of the factory carb kit and 2 control module replacements.Kinda of a work around to make it preform better.
I can't stress enough...The OEM fuel system on the 88/89 was just borderline.I just goosed it up a bit.




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