Air filter soaked with gas

[randy0211]

How can the air filter get soaked with gas? could it be from the carb or something?

[cheetahman]

Yup, needle valves don't hold back the fuel and it overfills the carburetor bowls, then the crankcase and the air cleaner fill up with gas.  Don't run it without checking the oil.  If there is gas in it it will be too thin and diluted. 

Or on rare occasions, the gas tank could have sprung a leak but I think that unlikely.  Run your finger under the seam in the rear of the tank and feel for wetness.

Also the overflow from the fuel neck runs down past the air box.  Verify that that overflow plumbing is intact.

[randy0211]

Yup, needle valves don't hold back the fuel and it overfills the carburetor bowls, then the crankcase and the air cleaner fill up with gas.  Don't run it without checking the oil.  If there is gas in it it will be too thin and diluted. 

Or on rare occasions, the gas tank could have sprung a leak but I think that unlikely.  Run your finger under the seam in the rear of the tank and feel for wetness.

Also the overflow from the fuel neck runs down past the air box.  Verify that that overflow plumbing is intact.

I know i have a leaking petcock, i saw a puddle by the bike,  but could it drain all the way there? (i just ordered a new petcock)

How would I verify the plumbing for the over flow?  I am guessing with out a doubt by a new filter?
thanks

[adidasguy]

Leaking tank petcock can be:
1. The o-ring in it - remove clip and replace o-ring
2. the oval o-ring between it and the tank
3. the 2 bolts require a rubber covered washer

Tank drain: look under the tank a few inches to the right of the tank petcock. That is the tank  overflow drain. There should be a hose going down to the ground. If not there, excess gas around the fuel cap can drain out and go onto the air box.

[Kerry]

The petcock may or may not be OK.  If it was in the PRIme position (see below) then there is no reason to suspect anything wrong with it  ... yet.




As cheetahman said, the problem could be with a float needle valve that is "stuck open".  The diagram below is for the '89-'00 models, but it should be OK for the current discussion.



The float needle in the carburetor is somewhere near the gasket between the float bowl and the rest of the carb body.  It is definitely below the height of the fuel coming from the gas tank.  If the frame-mounted petcock is set to PRIme, the only thing that keeps fuel from siphoning all the way through the carb is the float needle.  If that needle can't seat properly, the path is open and siphoning will commence.

Why wouldn't the float needle seat properly?  Well, there may be a bit of dirt/grit in the system which has gotten stuck between the needle and the edge of the hole that it pushes into, OR the needle surface may actually be worn out.  (Images from Clymer manual.)



Let's suppose that fuel indeed gets past the float needle and (over)fills the float bowl.  Where will the extra fuel go?  Well, once it rises up through the jet(s) into the carb body, it can go backward into the airbox ... ... and/or it can go  forward through the "rubber boot" into the associated cylinder.  If it goes into the airbox, it will proceed through the Airbox Drain Hose that adidasguy mentioned, and end up on the ground.

If the fuel goes toward the cylinder you could experience a VERY BAD result, depending on the position of the intake valve and the piston at the time.  At best, the intake valve will be closed and will prevent the fuel from entering the cylinder.  Next best, the fuel will enter the cylinder but drain past the rings and into the sump.  Worst case, the fuel will gather on top of the piston in between the intake and compression strokes, leaving no place for the fuel to go when you try to start the bike.  In that situation, parts can be damaged. 

The petcocks on many older bikes only had ON and OFF positions.  If (when) the owner forgot to turn the petcock to the OFF position after riding, they ran the risk of this "overflow" problem.  Leaving the GS500 petcock in the PRIme position runs the same risk.  Leaving  the petcock in the ON or REServe positions is supposed to prevent this problem, unless there is a tear in the diaphragm (or other problem) inside the petcock.

Questions?


EDIT: I forgot to address your question about the air filter itself.  If I recall correctly, someone on the forum *cough*Srinath?*cough* used to soak OEM paper filters in gasoline on purpose to clean them. 

[adidasguy]

Which petcock is he talking about?
The  one on the tank or the one on the frame?
i thought the one on the tank - as the frame one can't leak into the air box but the tank one could cause gas to get to the air box.

[cheetahman]

I am thinking there is a leak in the tank or at the petcock and it runs along the underside of the tank and then it drips into the airbox.

[Kerry]

Good point!  The process I described would only result in a "soaked" air filter if the Airbox Drain Hose were blocked, and a significant amount of fuel collected in the airbox.

Hmmm....