Bad Vacuum Advance?


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mclark38
Posts: 23
Joined: Thu Oct 25, 2012 8:53 pm
Location: Green Bay, Wisconsin
Motorcycle: 1982 GL1100I Interstate

Bad Vacuum Advance?

Post by mclark38 » Tue Sep 24, 2013 11:45 am



Hi guys,

I believe I have a bad vacuum advance or atleast a sticking valve of some sort inside of it. Last week my GL1100I ran great up until I came to a stop light and had to sit for a little bit. The bike finally warmed up while I was sitting there. When I took of it had very little power and ran very very rough and was jumping forward like it was just about out of gas. I got home and remembered that when I first got the bike and took it to a mechanic to get the carbs cleaned that he said something about he pulled off the vacuum line from the carbs and sucked on it which caused the valve to open in the vacuum advance, which made it run much much better. Ever since I pulled off that line and sucked on it to trip the valve its been running rough at low RPMs. Can I just shoot some kind of lubricant down the line to solve this or do i need to replace the whole assembly this winter?

Thanks,
Mike



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virgilmobile
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Re: Bad Vacuum Advance?

Post by virgilmobile » Tue Sep 24, 2013 12:54 pm

When I took of it had very little power and ran very very rough and was jumping forward like it was just about out of gas.
The vacuum advance part of the system does not operate at a low rpm.
This rough running from a idle is not related to it.
he pulled off the vacuum line from the carbs and sucked on it which caused the valve to open in the vacuum advance
This method is to test if the vacuum advance actually works..
The vacuum canister is a diaphragm sealed under the cap...do not spray anything into it...

Under normal conditions....(this is close)...
the 1100 has ignition timing at 10*btdc at 950 rpm...
it will increase up to near 23* btdc by the mechanical advance system..
it can increase to 38* btdc max combined mechanical and vacuum...
The vacuum is proportional to air flow.
It is ported before the throttle plate...
At a idle,there is no vacuum at the canister...
The timing changes as the vacuum on the canister increases to 1.6" and stops advancing at 3.5"
This vacuum will show only as the engine is revved up...never at a idle...

By your description...you have trash or water in the carb....
Start the bike from cold...idle only for 5-7 seconds..regardless of how bad it idles..do not rev it up...
Shut off the bike and lightly tap each header pipe...I'll bet 7 cents that at least one pipe is cold...

mclark38
Posts: 23
Joined: Thu Oct 25, 2012 8:53 pm
Location: Green Bay, Wisconsin
Motorcycle: 1982 GL1100I Interstate

Re: Bad Vacuum Advance?

Post by mclark38 » Tue Sep 24, 2013 1:54 pm

virgilmobile wrote: By your description...you have trash or water in the carb....
Start the bike from cold...idle only for 5-7 seconds..regardless of how bad it idles..do not rev it up...
Shut off the bike and lightly tap each header pipe...I'll bet 7 cents that at least one pipe is cold...
I'll give this a try after it cools down. Its been running great today. A little rough this morning until it was entirely warmed up but that's expected. Was going to start running Seafoam through is pretty soon before I put it away for winter anyways so maybe I'll start that right now.

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virgilmobile
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84 GL 1200 I

Re: Bad Vacuum Advance?

Post by virgilmobile » Tue Sep 24, 2013 2:04 pm

One day after my bike had been running flawlessly for a few months,it wouldn't fire on one side at a idle.(gl1500..2 carbs) but would fire at half throttle(just scary)....I finally got to work...

I opened the drain on the offending side,and with some compressed air blowing into the vent tube,it belched a teaspoon of water gunky stuff out of it....

Runs fine now..
Louisiana humidity condensed in the vent pipe and got sucked into the bowl...I've sense added a extension and a filter to that pipe...no further problems..

Remember we are now using that "special" gas...It can accumulate water in unwanted places.

mclark38
Posts: 23
Joined: Thu Oct 25, 2012 8:53 pm
Location: Green Bay, Wisconsin
Motorcycle: 1982 GL1100I Interstate

Re: Bad Vacuum Advance?

Post by mclark38 » Tue Sep 24, 2013 2:18 pm

virgilmobile wrote: Remember we are now using that "special" gas...It can accumulate water in unwanted places.
I've been trying to stay away from it as much as possible. About 95% of my gas is premium no-ethanol

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

Re: Bad Vacuum Advance?

Post by virgilmobile » Tue Sep 24, 2013 2:21 pm

Great...Hopefully what ever it was got sucked through the system...Mine was so bad it plugged the slow speed jets...

amonera
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Re: Bad Vacuum Advance?

Post by amonera » Sun Mar 03, 2019 2:55 pm

Hi Guys,

I am having problems with my 81's GL1100. It has been running a little bit rough recently, so the symptoms are:


In cold works like crap, some "bangs" and misfires i would say, it has a lot of hesitation to accelerate, i need to rev it and hold the clutch in order to start moving (only in cold)... and when is worm, i have a small hesitation when accelerating lets say.. from almost stop in second.. like there is a moment that the things are in synch and then it goes and come back...

In theory the carburetors were done by the previous owner so, for the moment i am trusting... but for what i have seen in this bike there is a limit to trust.... but if i dont trust.. is better to sell, travel back in time, and buy a new one.

Now, the test:

@virgilmobile: I have check the cold start 7 second test... 4 exhaust are worm but there is one slightly less worm, seems.. from 45 C.. to maybe... 40... not much and i am aware that there is lower compression in this cylinder compared with the rest (130 vs 150ps)

I have disconnected the vacuum advance in idle.. and sealing the carburetor with a blocked vacuum hose and this seems to make the bike worst, a little bit in idle, but definitively rougher when accelerating...

I have also suck in the vacuum hose to the advance and i can feel something there moving... which kind of improve for a second and then goes back to rough...

Now, the main note... If i suck in to the advance... the advance membrane is not keeping the vacuum.. i can feel myself getting a little bit of air out of the vacuum advance... I am not sure how sealed this is suppose to be... but is not holding vacuum for sure.

I see that the vacuum advance there is a flat screw in the cup, i haven't manage to know what this is for, but in the ring and in the screw there is some grease, like if it has been leaking out of the screw and/or surrounding ring.

so tell me guys if you can if i need to find a way to open the ignition unit, or i should try with the carburetors?

best regards :)

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newday777
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Re: Bad Vacuum Advance?

Post by newday777 » Thu Mar 07, 2019 5:38 pm

Having been involved with these carbs since 2009 my first geuss from your description is in the carbs, either plugged fuel ports(there are tiny ones that (improperly) 'cleaned' by spray methods are not clean), vacuum leaks(base of intake are orings) or electrical weakness in spark plug wires and caps(they screw on, get corrosion in the wires, compromised spark especially when cold/damp conditions.
The vacuum advance you can check, suck on it to listen for movement. Check this first, then plug wires and coil output(tests in the service manual)
If those test good then Start with a proper carb cleaning, not spray cleaning. Ultrasonic or boiling after fully stripped bare.
amonera wrote:
Sun Mar 03, 2019 2:55 pm
Hi Guys,

I am having problems with my 81's GL1100. It has been running a little bit rough recently, so the symptoms are:


In cold works like crap, some "bangs" and misfires i would say, it has a lot of hesitation to accelerate, i need to rev it and hold the clutch in order to start moving (only in cold)... and when is worm, i have a small hesitation when accelerating lets say.. from almost stop in second.. like there is a moment that the things are in synch and then it goes and come back...

In theory the carburetors were done by the previous owner so, for the moment i am trusting... but for what i have seen in this bike there is a limit to trust.... but if i dont trust.. is better to sell, travel back in time, and buy a new one.

Now, the test:

@virgilmobile: I have check the cold start 7 second test... 4 exhaust are worm but there is one slightly less worm, seems.. from 45 C.. to maybe... 40... not much and i am aware that there is lower compression in this cylinder compared with the rest (130 vs 150ps)

I have disconnected the vacuum advance in idle.. and sealing the carburetor with a blocked vacuum hose and this seems to make the bike worst, a little bit in idle, but definitively rougher when accelerating...

I have also suck in the vacuum hose to the advance and i can feel something there moving... which kind of improve for a second and then goes back to rough...

Now, the main note... If i suck in to the advance... the advance membrane is not keeping the vacuum.. i can feel myself getting a little bit of air out of the vacuum advance... I am not sure how sealed this is suppose to be... but is not holding vacuum for sure.

I see that the vacuum advance there is a flat screw in the cup, i haven't manage to know what this is for, but in the ring and in the screw there is some grease, like if it has been leaking out of the screw and/or surrounding ring.

so tell me guys if you can if i need to find a way to open the ignition unit, or i should try with the carburetors?

best regards :)

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ekvh
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Re: Bad Vacuum Advance?

Post by ekvh » Thu Mar 07, 2019 9:04 pm

Description sounds like a possible stuck or sticking slide. The one point it runs well is when the other three slides are the same as the one that’s stuck. (Could be two slides) but then it would be really rough.

My old 77 would do that if I didn’t give the gas MMO. Of course a proper cleaning might have done it too.

The slides can be removed and cleaned/polished without full extraction of the carbs by sliding the rack left and right as needed.



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