I think it's a vaccum line issue...

[Sojourner]

Steve rebuilt and sync'ed my carbs just over a week ago. New O rings, thorough dipping, the whole 9. So that should rule out carb gunk and sync issues.

Bike has ran fine up until yesterday evening and today. Yesterday evening it seemed to bog a bit. Sort of a stutter. Also noticed that at some stoplights the idle would noticeably be up from 1100. Next stoplight 11 on the money. This morning I went out to start the bike ('80 GS1100E) and it cranked and cranked and no love. Wore down the battery, charged it up, and after more cranking it finally started. "Weird" I thought. "Maybe it was just the morning dew?" since it gets stored outside under a cover and a tarp normally but not last night. Anyway, drove it into work and parked it. Still seemed a tad grumbly at times, but overall the ride in was uneventful. So I just went out to the parking garage to hop on the bike and get some lunch... Lot's of cranking, but no starting.

So I did a little troubleshooting. Took the tank off, disconnected the hoses to the petcock, and noticed the main fuel line was bone dry. Now correct me if I'm wrong, but the petcock works in sort of a push/pull fashion- the #2 carb pushes air into the vaccum line and that allows the fuel to come out the fuel outlet and into the fuel line where the carbs do their thing. Correct? Operating under this assumption, I gave the vacuum line and the fuel line a visual inspection and all looked good. So I gave a little puff/suck on the vacuum line. Should I be able to blow into the vacuum line easily? It seemed it was exiting in the linkage bit where #1 and #2 meet up judging by the little bubbling spot. Negative pressure (sucking) was like the hose wasn't hooked to anything at all.

Again- I might be way off base. Any insight would be EXTREMELY helpful. My working hypothesis is that it won't start because it's not getting fuel, and that's happening because the pressure isn't regulating thanks to something with the vacuum line. Or is it a gas cap seal issue throwing the whole pressure thing off? Half a tank of gas so the cap shouldn't really come into ply (petcock submerged and all). Help please?

Oh, and I called the wife so at least I have a ride home.

 

[loud et]

One fact is that if you suck on the petcock line it OPENS the fuel flow.
If you blow on the petcock vaccuum line it should be closed, ie: cant blow into it.

With the vaccuum line hooked to the #2 carb you can blow and suck with no resistance. That is normal. Only when the engine cranks does it then start a vaccuum on the #2 carb and petcock vaccuum line.

 

[loud et]

Turn it to prime and try to start it like that also. That may get the system flowing again.

 

[Agemax]

the petcock is vacuum operated, the line going to the petcock from the engine sucks a diaphragm open which allows fuel flow. if you suck on the line to the petcock and feel nothing, the diaphragm could be split, caising it to fail to open.

try running it on prime, it should run fine, if it does then it confirms a faulty petcock

 

[Sojourner]

Thanks for the replies. The "suck test" was the line connected to the #2, not to the petcock. I'll try it connected to the petcock and see what happens.

1) Any reason for a petcock to just up and bite the dust like that?

2) Might sound silly, but the tank has been repainted, along with the outside of the petcock, so many times it's hard to read. Currently the little flathead screw looking selector is pretty much left-right horizontal. Is it on prime already then?

3) Would fuel starvation cause the idle to climb like it did yesterday?

 

[loud et]

As you likely know..... when you suck on the petcock (and hold the vaccuum) the fuel begins to flow.
When you stop sucking the fuel should stop within a couple seconds.

I always test my petcock dry.....sucking and releasing, you should hear the diaphram clicking back and forth. Then, with tank removed i suck on tje petcock till fuel begins to flow into a cup/ container.....then release the vaccuum and watch for the fuel to stop within a second or two.

Its like a prerequisite test i do before i even use it on a bike
Rules out obvious problems.

An 80 petcock can be easily disassembled and cleaned up.
Its worth a looksy. And a test like i described is certainly in order.
Fyi, there is an e bay petcock for our bike for 45 bucks. Brand new, oem style, its the one i got. It works beautifully.

 

[Agemax]

Thanks for the replies. The "suck test" was the line connected to the #2, not to the petcock. I'll try it connected to the petcock and see what happens.

1) Any reason for a petcock to just up and bite the dust like that?

2) Might sound silly, but the tank has been repainted, along with the outside of the petcock, so many times it's hard to read. Currently the little flathead screw looking selector is pretty much left-right horizontal. Is it on prime already then?

3) Would fuel starvation cause the idle to climb like it did yesterday?

1, yes the diaphragm could split, or even stick at any time.
2, not sure about those petcocks.
3, yes, lack of fuel in the float bowls would give a lean mixture at idle, causing the revs to rise

 

[Guest]

Isn't the vacuum on #3 or is it different on CV carburetors?

 

[Sojourner]

#2, 2nd from left when seated.

Tried blowing into the vacuum line (connected to petcock) and it was like the big bad wolf up against the brick house. I blew and it wasn't going anywhere. Sucking created a touch of vacuum but was easy enough. I didn't disconnect the fuel line to see if anything was coming out since I was still in the parking garage.

Next guess/step?

 

[tom203]

#2, 2nd from left when seated.

Tried blowing into the vacuum line (connected to petcock) and it was like the big bad wolf up against the brick house I didn't disconnect the fuel line to see if anything was coming out since I was still in the parking garage.

Next guess/step?

Forget blowing nonsense- disconnect fuel line at petcock ,get beer can to catch fuel, suck on vac line connected to petcock- fuel should flow out and stop when you stop sucking.

 

[Sojourner]

Lots of blowing and sucking talk... Think this thread will get banned?

Seriously though, I couldn't do a lot since the bike was in the public parking garage downtown. No beer can on hand. I fully intend to delve deeper, but still need to get the bike home at this point.

So what's the possible outcomes- If it spits out gas, then suspect vacuum line? No gas, then suspect the petcock?

 

[loud et]

Ur gonna have to test it to see if sufficient fuel is coming out when you apply vaccuum to the petcock. A slow to medium steady stream of fuel should come out.
If it does not, you may be starving your carb bowls.
The petcock and or screen inside tank may be restricting flow.
If you never looked, you just dont know.

As is said......" to measure is to know"

 

[loud et]

Lots of blowing and sucking talk... Think this thread will get banned?

Seriously though, I couldn't do a lot since the bike was in the public parking garage downtown. No beer can on hand. I fully intend to delve deeper, but still need to get the bike home at this point.

Get a small screwdriver and try prime setting to encourage fuel flow to assure the bowls are filled.

 

[tom203]

Unfortunately, bike won't start without fuel, so you need to determine if petcock is actually flowing fuel. You won't spill much in testing- and you might get a bit part in a HBO movie!

 

[Sojourner]

But which way is prime? Should the slit be horizontal or vertical?

 

[tom203]

But which way is prime? Should the slit be horizontal or vertical?

I vote vertical,but try in both ways- still needs a vac pulse to get going even in prime.

 

[Steve]

Isn't the vacuum on #3 or is it different on CV carburetors?

It is different. On the VM carbs, it is inded #3. On the BS carbs it is on #2.

Forget blowing nonsense- disconnect fuel line at petcock ,get beer can to catch fuel, suck on vac line connected to petcock- fuel should flow out and stop when you stop sucking.

Just wondering why I might have to go out and buy the first beer I have every bought, just so I can dump it out to check fuel flow. :-k

Yeah just about any container that will withstand gaoline should work.

Get a small screwdriver and try prime setting to encourage fuel flow to assure the bowls are filled.

Keep in mind that the "dreaded '80 petock" works a bit differently than most.

On all the others, you simply turn the petcock lever to the PRIme position and gas flows. On the "dreaded '80 petcock", you have to turn the petcock to PRIme (slot will be vertical) AND apply a 'puff' of vacuum. After that, fuel will flow until the petcock is turned to the RUN position or the supply of gas is exhausted. That means that if you are trying to prime the carbs after the bike sits for a while, you turn the petcock to PRIme, bump the starter so the engine spins a couple turns (to ensure that #2 has done its intake cycle at least once), then turn the key off while the carbs fill.

.

 

[tom203]

Just wondering why I might have to go out and buy the first beer I have every bought, just so I can dump it out to check fuel flow. :-k

.

Buy one? all parking garages have beer cans free for taking-

 

[Dogma]

If the petcock is original, it probably needs replaced. On the prime setting you shouldn't be able to suck air through it. After the valve opens, there should be no more air flow (on prime). Anything else is a faulty '80 petcock that won't stay open long enough to feed the bike. Also, the faulty part can't be fixed or rebuilt. It's not a cleaning issue, it's the little plastic valve thing you turn with a screwdriver. Maybe some chemist knows how to make it swell up and seal again.

 

[Guest]

I have an 80 tank on my bike. The little screw slot is not very accurate on the valve. Plan on pulling the fuel line when you have turned the slot back to the horizontal position for vacuum only operation. You may still have to tweak it a little bit to stop the fuel flow. It can look perfectly horizontal and still flow fuel. The only way to be certain it is to check it with the fuel line off so you don't end up with a crank case full of gas.