Need help....unknown problem!

[Badger]

the bike started to behave strangely.

I think more information on how it was behaving would aid troubleshooting.  :dunno:

[diamond_lady]

the bike started to behave strangely.

I think more information on how it was behaving would aid troubleshooting.  :dunno:

Yeah, sorry... .... the bike started to hesitate, like there wasn't enough gas in the tank (I guess you all know what it feels like   )

[Badger]

the bike started to behave strangely.

I think more information on how it was behaving would aid troubleshooting.  :dunno:

Yeah, sorry... .... the bike started to hesitate, like there wasn't enough gas in the tank (I guess you all know what it feels like   )

Have you seen all the threads on fuel starvation?  Do you have symptoms like those?  Seems to be a common problem.

[Toledo Jim]

.....I think the tank is half-filled, and I had to put it to res because the bike started to behave strangely. I put it on res and it solved the problem.
Question is: why the hell this happens?

I just bought it used (it's a '91 GS) with few kilometers so I think that maybe the guy left it some time unused.

Water in the tank from condensation is my guess.
I suggest draining tank totally and filling it with fresh gas.

http://gstwins.com/forum/viewtopic.php?t=20114

[Badger]

Water in the tank from condensation is my guess.
I suggest draining tank totally and filling it with fresh gas.

http://gstwins.com/forum/viewtopic.php?t=20114

Why would switching to RES make it go away?  The way I understand it, the reserve feed pulls from lower in the tank...thus if ON was drawing some water, RES would probably draw -all- water, since the water would settle below the fuel.  I'd also think that if there was that much water, you'd have a heck of a time getting it started after it had been sitting...but I could be wrong on where the fuel draws from.

[Toledo Jim]

Water in the tank from condensation is my guess.
I suggest draining tank totally and filling it with fresh gas.

http://gstwins.com/forum/viewtopic.php?t=20114

Why would switching to RES make it go away?  The way I understand it, the reserve feed pulls from lower in the tank...thus if ON was drawing some water, RES would probably draw -all- water, since the water would settle below the fuel.  I'd also think that if there was that much water, you'd have a heck of a time getting it started after it had been sitting...but I could be wrong on where the fuel draws from.

Like I said, it's a guess. :dunno:  But it would be inexpensive to check.

Also, Badger, or anyone else, can you answer the question asked in this thread?
http://www.gstwins.com/forum/viewtopic.php?p=187662&highlight=#187662

[diamond_lady]

Water in the tank from condensation is my guess.
I suggest draining tank totally and filling it with fresh gas.

http://gstwins.com/forum/viewtopic.php?t=20114

Why would switching to RES make it go away?  The way I understand it, the reserve feed pulls from lower in the tank...thus if ON was drawing some water, RES would probably draw -all- water, since the water would settle below the fuel.  I'd also think that if there was that much water, you'd have a heck of a time getting it started after it had been sitting...but I could be wrong on where the fuel draws from.

I agree with you. The tank has already been cleaned; maybe there's some dirt in it. Seems like ON doesn't draw enough fuel.
The bike never had problems on starting

[diamond_lady]

Ok here's the update:

- I checked the spark plugs, the left one was really black....I cleaned it and set the right distance between the two electrodes (I don't know if it's right in ienglish, be patient   ).
It seemed to hae solved the problem.....now the little lady goes like a wonder, I swear, I went riding this morning and it was fantastic. Never showed an hesitation, driving was fantastic and very easy, really really different from yesterday.

But I suspect that someone made some mess with the fuel lines, it's too strange that I have to put it on RES after only 70-80 km (with full tank).
Tomorrow morning I'm gonna open it and I'll let you know  

[scratch]

I'm glad the sparkplug was an easy fix. Was the other sparkplug in the same condition? If not, then the float levels may be different between the two carburetor float bowls, and the one sparkplug may foul again. Another thing to do is to sychronize the carburetors, so that they both open at the same time. A mechanic with a set of vacuum guages should be able to do that.

I think the tank is half-filled, and I had to put it to res because the bike started to behave strangely. I put it on res and it solved the problem.
Question is: why the hell this happens?

Either the tank was not completely full, or the GS are known for leaving almost a gallon (I'm guessing that's 2-4 litres) even after switching to RES. So the motor may not start, even though you see enough fuel.

[diamond_lady]

I'm glad the sparkplug was an easy fix. Was the other sparkplug in the same condition? If not, then the float levels may be different between the two carburetor float bowls, and the one sparkplug may foul again. Another thing to do is to sychronize the carburetors, so that they both open at the same time. A mechanic with a set of vacuum guages should be able to do that.

You're right, the other sparkplug was perfect, so tomorrow I'll clean the carbs and see if it helps.
But I'll wait 'til the sparkplug fouls again before going to a mechanic...am I wrong? The bike is doing really good at the moment.

For the tank problem....mmm I guess that is not my case. I swear there was too much fuel in the tank to make it necessary switching to res.... this thing has already happened twice: after about 50 miles the bike starts to hesitate, and I need to put it to res. Then she behaves like normal and I can go on for at least other 50 miles (and more..). :dunno:
Anyway the previous owner put his hands in the tank to clear some rust, so I want to look and see if he's done some major mistake... :x

[scratch]

Then either the vacuum line to the inside of the left carb is not connected to the fuel selector/switch (petcock), or you are suffering from fuel starvation. I'm leaning toward the vacuum line because it sounds like it happening at the same time (every 50 miles); what I suppose is happening is that the engine runs on just the fuel in the fuel lines and the floatbowls, which gets you 50 miles til they run dry, because the vacuum actuated diaphragm in the fuel switch is being opened by the vacuum from the left carb/cylinder, allowing more fuel to get by.

I am conjecturing, of course.

[John Bates]

How about this:

The carbs are running rich and the RES fuel line is partially blocked.

So:

When the bike starts running like crap (carbs running rich),
she switches to RES and the bike runs great because the fuel supply returns to normal.
(partially blocked RES line offsets the rich condition).

Just a guess. :dunno:

[diamond_lady]

both your opinions are very interesting.... It's 10 a.m. here, at noon I'm goona open the bike to understand more, so I'll let you know who's the winner!  

[diamond_lady]

Here I am.
I opened the bike and checked everything I thought might be the cause of my problem.
First of all I cleaned the carbs, there was some water and dirt into.
Then I inspected the fuel lines, they are ok there was no need to replace them, I only cleaned them. The sprocket is ok too.
I took off the tank and cleaned it; there was some dirt and rust in it. I took off the fuel chicken (at least I think this is its name...) and its filter, it was very dirty....maybe that could be the reason why fuel wasn't always coming cinstantly.
I put some liquid gasket around the filter because gas was dripping from the two screws that hold the fuel chicken at the tank.
Then I put everything back on, watching carefully to put the fuel lines in the correct way. The bike goes like a wonder, my first impression is that there is no more 'fuel starvation' (I'm using this expression although I know it's not totally correct), gas was coming fluently without any break.
In the next days I'm gonna go to the mechanic and sync the carburators.....not much I can do expect wait and see if the problem shows up again!! Am I wrong?  :dunno:

[diamond_lady]

When the bike starts running like crap (carbs running rich),
she switches to RES and the bike runs great because the fuel supply returns to normal.
(partially blocked RES line offsets the rich condition).

I think you could be right. The res fuel line was dirty, the filter of the fuel chicken was really dirty (the filter of 'the res part').
Well at least I think that cleaning everything must have made it work better...

[John Bates]

.............. Am I wrong?  :dunno:

I think you are going about it logically.  

Hope you solved the problem.