QuestionI bought this bike years ago and this has been a persistent problem which has gotten worse, and now I have not even tried to start the engine in over 4 years.
To make a long story short, carbs will not stop gas flow out over flow tubes when engine is running. Plugs get fouled and engine bogs out. So I pulled off fuel bowls and sprayed carb cleaner up in the meter jet nozzle. Gently used compressed air to blow out. Put in new needle and seats, no change. Pulled back apart. With pet cock on, gas flows with float/s down. When floats held up, gas stops.
Checked float drop and height, weighed floats, not all do this leaking stuff, even put in bowl of gas to see if indeed float would float, yep.
Back together and no change. Fire it up and the flow starts. I have taken the pet cock out of the tank to check for rust deposits and none, tank is clean.
It is like when the gas is on and the engine is running the floats do nothing at all. Gas just pours out.
Any help or advice would be greatly appreciated. I could pull the carbs off and tear them down and soak them, but would it do any good?
AnswerHi Jerry,
It sounds like you have tried a few things
to solve this carb problem so I will not
go into those things too much.
I have a few ideas other than a good carb soak
which it may need after so long parked.
Yamaha carb cleaner is good because it does
not harm rubber and plastic parts.
The jets will need to be physically checked
with a piece of smooth guitar string or
such to make sure the idle and main jets
are totally clear of fuel varnish.
If you are sure your floats have no pin holes in
them and the fuel height is not too high (fuel should
be about a millimeter below the float bowl
gasket surface) then I have a few other ideas.
1. Some float needle valves are metal and can be
mated to the seat with some fine grinding compound.
2. Some float needle valves use o-rings or gaskets
under them which if faulty or missing can leak fuel into the carb
even when the float needle is closed by the float.
I believe you said you checked these for leakage.
3. Fuel tank cap air breathers can plug up causing air pressure
to build up in the fuel tank causing fuel to leak.
Either check the cap or add a new air vent checkvalve to the tank.
4. Air vent passageways inside the carb may be plugged
with old fuel varnish. This does not allow air to vent
from the float bowl so can push fuel out overflow instead of
venting air up above. It is like an air lock in the float bowl.
Soaking overnight in the Yamaha carb cleaner may fix this.
5. The float bowl has a brass overflow tube that the
fuel goes through when the bowl is overfull.
These brass tubes can develop cracks around the
bottom or sides of the tube allowing fuel
to drip even when the bowls are not overfull.
You may be able to epoxy or solder these up.
Here is a GS carb cleaning guide:
http://www.thegsresources.com/files/GS%20Carb%20Cleaning%20Series.pdf
Good luck!
Wayne S.
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