88 gl1500 off idle hesitation theory


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virgilmobile
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88 gl1500 off idle hesitation theory

Postby virgilmobile » Thu May 31, 2012 3:32 pm



My 88 is annoying.Not every time but it will buck when accelerating in 1st.
I just dealt with this because I've read so much about mods that did not address the problem or fix it.
I "think" I have the correct answer.....here goes.

When I serviced the carbs,I also checked the accelerator pump action.Yes they squirted fine.

I noticed in driving that if I hold in 1st gear and run for a few minutes around a parking lot at 1100 rpm then try to accelerate it will buck on me.Same thing if I idle up slow to a light,using no throttle movement.
The strange part is that I can go through a couple of gears,return to a idle and it will pull off just fine.

What I deduced....
While NOT running the throttle up and down,the check valve inside the riser tube for the accelerator pump is leaking fuel back out of the accelerator port.
Open the throttle and there is no squirt of fuel and it bucks.
The next throttle stroke fills the accelerator tubes back up and all is well until the next idle time.

I'm gonna rip the covers off tonight to look at this.
I expect that I should have some accelerator pump fuel squirt after setting for several minutes,If I don't,I;m gonna look really close at the check valve system.
I'll post some pictures and my findings ASAP as I've read about this complaint a lot.

Feel free to add to this for more info about the problem or solution.
And yes,I've tried everything else.
This is persistent and can be duplicated every time.It just took a few hundred miles to identify the pattern.



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Re: 88 gl1500 off idle hesitation theory

Postby WingAdmin » Thu May 31, 2012 4:08 pm

It sounds like a valid theory to me. Let us know what you find once you crack it open.

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Re: 88 gl1500 off idle hesitation theory

Postby HALBUDD » Thu May 31, 2012 6:24 pm

Hey Virg just saw your new avatar guess littlebeaver is getting to you guys,but WingAdmin has not X his old bike yet HAHA Hal
A woman that can use tools is worth her weight in gold !!

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virgilmobile
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Re: 88 gl1500 off idle hesitation theory

Postby virgilmobile » Thu May 31, 2012 10:39 pm

Here's the results.
The accelerator pump does not work like I expected.I have to really crank the throttle to get any squirt out of it.
Sometimes it gives a few drops just above idle but after a few times it quits.
I did tear the pump apart.The diaphragm is hard and surfaced cracking but does not leak.
The check valve in the coupler tube is OK as are the "O" rings.
The lower check valve does not seal well.I'm going to soak it and get a kit for it.Here's the video...
I have taken more videos and a bunch of pictures too.
Even after just cleaning,the pump will not deliver fuel on a slow push.I have to pump it at least half way down,or 1/2 throttle to get any flow from it.
I'm hoping the kit will restore it.???




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Re: 88 gl1500 off idle hesitation theory

Postby WingAdmin » Fri Jun 01, 2012 9:33 am

That video is definitely wrong, as you know. So you suspect the pump is operating, but due to a bad check valve, is just pumping backward, instead of out through the nozzle?

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Re: 88 gl1500 off idle hesitation theory

Postby virgilmobile » Fri Jun 01, 2012 11:39 am

I'll post some more stuff later as I compile the data.
After more work,I cleaned the check valve and reinstalled it.the squirt is better,however there is none at a slow throttle movement.I have to snap it to get it to squirt.
Obviously you dOn't snap the throttle in 1st gear on this bike.
I also found a reason for the action of the pump.There is a pressure bleeder port that bypasses the check valve.by design,this pump cannot squirt on a slow roll of the throttle.
I'm gonna video the current bench test,plug the bypass port and test again

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Re: 88 gl1500 off idle hesitation theory

Postby virgilmobile » Fri Jun 01, 2012 1:31 pm

Here's the picture.I plan to measure the pump action then plug the bypass port and test it again before I install it.
Oh,by the way.This pump is only on the 88-89.There different on 90 and up....Maybe someone figured it was a bad design.??And it's no longer available either.

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Re: 88 gl1500 off idle hesitation theory

Postby goldminerusa » Fri Jun 01, 2012 8:02 pm

Seems to beg the question, can 90 and up accelerator pumps be fitted to 88-89 carbs and /or can 90 and up carbs be used on an 88-89? Just asking, i own an 1100 but want a 1500.

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Re: 88 gl1500 off idle hesitation theory

Postby virgilmobile » Fri Jun 01, 2012 10:47 pm

I've heard the carbs can be replaced with the 90's year,and I also wonder if the accelerator pump is different in design and/or will fit the 88.
I finished the project late tonight with seemingly good results.it will be Saturday afternoon before I can run it enough to verify if it made a difference.

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Re: 88 gl1500 off idle hesitation theory

Postby VTBikeman » Sun Jun 03, 2012 12:01 pm

I may have the same problem on my 89. Please keep us posted on your results.
Thanks

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Re: 88 gl1500 off idle hesitation theory

Postby virgilmobile » Mon Jun 04, 2012 12:59 pm

All the work ant testing is done.
The end results.....My hesitation/bucking/stutter that jerks the bike real hard pulling away in first is 80% gone.
The cause was a bad check valve in the bottom of the accelerator pump.
I believe it will never completely be eliminated without replacing the carbs with a 90 year model or later including the ECM,and,CCM modules.
I think the first attempt(88,89) was poorly designed.
I have somewhat successfully improved the problem by just dumping more gas down the throat of the carb when it needed it.Not the best fix,but cost wise,I can live with it .
Here's all the details....


At the beginning there was little action.
removing the pump.leaving the carbs on the bike
removing the pump.leaving the carbs on the bike
separating the pump
separating the pump
diaphragm is fair.a bit hard but no leaks
diaphragm is fair.a bit hard but no leaks
first look inside.nothing sticks out.....wait for it...
first look inside.nothing sticks out.....wait for it...



Checking the check valve for real operation



This thing is leaking from everywhere
a little heat needed to free the valve
a little heat needed to free the valve
now it's out...Yuck..what a mess.
now it's out...Yuck..what a mess.
tapped in a drift pin to tap it out and clean it
tapped in a drift pin to tap it out and clean it
Q Tip and polish,stretch the spring a bit
Q Tip and polish,stretch the spring a bit
reassemble the valve
reassemble the valve

After reassembly,i found 2 bypass ports.No wonder,with the bad check valve AND the bypass ports I couldn't get and compensation from the accelerator jets.


So I soldered the bypass port shut
So I soldered the bypass port shut
with the help of the propane torch I plugged the second one too
with the help of the propane torch I plugged the second one too

Now after it's all back,I tested it.Still not as much squirt as I really wanted but a great improvement from nothing.


So I took it for a test drive.Yup it's much better.
Just a little hesitation once in a while...At least it doesn't buck me now.


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Re: 88 gl1500 off idle hesitation theory

Postby VTBikeman » Wed Jun 06, 2012 9:00 pm

Thank you very much for this. Really useful.

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Re: 88 gl1500 off idle hesitation theory

Postby dingdong » Thu Jun 07, 2012 8:53 am

Good work Virgil. Now I am wondering if the "hard" diaphragm might be causing the rest of the problem??
Tom

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virgilmobile
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Re: 88 gl1500 off idle hesitation theory

Postby virgilmobile » Thu Jun 07, 2012 9:20 am

It's very possible.The thing is original and very stiff.
The accelerator pump,on the final,works but I really expected a bit more squirt.
I've ordered a new because I don't know how it should work.As in how fast it can be pushed down and recover.
I'm hoping that the stiff rubber diaphragm is just slowing down how much and how fast it will deliver fuel.

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Re: 88 gl1500 off idle hesitation theory

Postby virgilmobile » Thu Jun 07, 2012 12:15 pm

Poking around on the net,I found the accelerator diaphragm for $35.
I stumbled on this site.$15.
Anybody been here?
http://www.siriusconinc.com/pro-detail. ... uct_id=990

Just found out there in Canada.Long wait.

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Re: 88 gl1500 off idle hesitation theory

Postby VTBikeman » Thu Jun 07, 2012 11:41 pm

Virgilmobile,

I like to know as much as I can before I go after something. I have some questions.

Is the check valve slug all metal or is there a rubber seal around the edge?

How did you stop the leaking around the edge of the check valve slug where it fits the body or did you?

Also what did you do to the check valve piston to make it seal?

Thanks in advance from Vermont.

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Re: 88 gl1500 off idle hesitation theory

Postby virgilmobile » Fri Jun 08, 2012 8:50 am

I removed the check valve from the casting with needle nose pliers,heat and a lot of wiggle and pull.
Once out,I used a drift pin(flattened nail would work) and supported the valve with a socket.
Insert the drift pin and push the ball all the way up,give it a little tap and the whole thing comes apart for cleaning.A good soak to remove the gas varnish and tap it back into place.

If your's is leaking,you might try to soak it first and just blow it out.

As far as the leak.
The check valve was laid on the vice BEFORE I put it back into the casting.
I used a 7/16 socket and ground down a slight taper on the end.Just enough to fit inside the lip of the check valve.
Again just a few taps with a hammer swelled the valve at the top 0.010" larger than the bottom.
Using heat to expand the casting,I tapped it back into place.
Be careful.If you smash it all the way down,it will contact the brass insert in the bottom and completely shut off the fuel.So I suggest either marking it's original depth or scribing it into the inside of the casting.
By all means replace the diaphragm too.I think they get stiff.

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Re: 88 gl1500 off idle hesitation theory

Postby ttiger » Mon Jun 11, 2012 12:14 am


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Re: 88 gl1500 off idle hesitation theory

Postby virgilmobile » Mon Jun 11, 2012 8:25 am

I've read the low speed drive ability report and the factory mods.Mine was never done and those who have had it done report mixed results.Some just enough improvement to stop complaining.

Mine is at that point,I just found a local that has a new K&N diaphragm kit.I paid $50 for it.
I'm hoping with it and plugging the 2 bypass holes it will give me the squirt I need to stop the little hesitation I still occasionally have.
The local has a repairable carb set from a 96....he wants $600 for them.
Well he wants.....

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Re: 88 gl1500 off idle hesitation theory

Postby VTBikeman » Mon Jun 11, 2012 12:49 pm

Can anyone confirm the service bulletin only pertains to the 88 and not the 89 Wing?

Thanks

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virgilmobile
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Re: 88 gl1500 off idle hesitation theory

Postby virgilmobile » Tue Jun 12, 2012 3:12 pm

Sorry,I can't confirm this,however i understand that the 88-89 were identical and HONDA changed the carb system in 90.
All the parts info separate 88-89 from the rest of the years when it comes to the carb parts.
I see a lot of "for 88-89 only" stuff out there.
Does that make us SPECIAL or just isolated.?

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Re: 88 gl1500 off idle hesitation theory

Postby VTBikeman » Wed Jun 13, 2012 1:39 am

I'm feeling SPECIAL right now.
My 89 is still a beast with 116K on it. I just ran some more highly concentrated Seafoam thru the gas tank. It is running pretty well but not perfect. I think the slow speed jets might be a tad small. It opens up when I get the throttle about 40% open and up. And it greatly prefers to be warm.

I haven't had the time to really go after carbs. I always feel like they are next to impossible to fully diagnose and no fun to pull or work on. There is very little info on the proper operation or how the work online and usually the fix is a complete teardown rebuild.

I just spent 4 hours changing some dash lights on the beast. Everything takes time and I have tires, rotors and pads to get to next.

Again thanks for everything you have cooked up. If you get the service bulletin upgrade let us know. Does Honda still do it?

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Re: 88 gl1500 off idle hesitation theory

Postby virgilmobile » Sat Jun 16, 2012 2:32 pm

Ok,I'm almost satisfied.98% of the hesitation is gone.In a 50 mile ride around town,once it did give just a slight delay when I cracked the throttle from 1200 rpm in first.But nothing like it used to buck me and clunk the transmission.I'm going to get the 4* timing wheel for that.
Here is what I did to reduce the off idle hesitation.There are 3 videos of the accelerator pump.
1st was at it's worst.
2nd after plugging the return ports and cleaning the leaking check valve.
3rd is after replacing the diaphragm.
The last test run made the acceleration so aggressive that my low fuel light stayed on till I leveled off on OD at 60mph.
You can see here that the pump is almost not working at all.


After I plugged the return ports and cleaned the check valve,it did improve quite a bit,


Finally,after replacing the diaphragm,It really squirts like I wanted.Better than the factory design.


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Re: 88 gl1500 off idle hesitation theory

Postby VTBikeman » Sun Jun 17, 2012 1:40 am

Let us know if this impacts your mileage MPG's.

Again thanks for posting all the info.

Went through my 3rd can of SeaFoam and it is running smooth. But could use some work.
Maybe you can help. It runs fine but when I exit a big highway on a downward sloped exit ramp the engine will stall. I can keep it alive with some throttle or restart it from coasting but it is a pain. My first thought is vacuum leak but haven't chased it yet. Any ideas or had this one?

Thanks.

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Re: 88 gl1500 off idle hesitation theory

Postby virgilmobile » Sun Jun 17, 2012 10:13 am

Mine did the exact same.I replaced all the bad vacuum hoses.It seems to deteriorate at the sharp 90* bend.I found a total of 7 bad spots.
One is under the carbs,below the rubber mat,2 on the carb body,2 on each left and right manifold.
I'm due to fill up again.I've been driving in town mostly and I've been getting 33 mpg.
I expect it to go down a little just because I'm always twisting the throttle.
The open road should be the same.
Here's my final report...viewtopic.php?f=6&t=11970




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