Fuel tank breather system

[hamousher]

Hi, I need help with the fuel tank filler cap breather system. I previously thought I had an oil leak, as there were small puddles on the ground under centre stand. Now looks like this deposit is coming from the fuel tank breather pipe. In warm weather fumes can be seen coming from the pipe, after a while the fumes seem to condense and there is an oily type substance dripping from the pipe onto the ground under. Eventually the puddle can become 4 inch in diameter. I dismantled the filler cap to check the airway through it. Now I don't know if all is well. Has anyone out there taken the filler cap apart and can give me some advice please. After removing the lock by taking out the two screws, under the lock is a round plate with 4 holes. 2 of the holes are for the fixing screws. Under the plate can be seen 2 recesses, in 1 there appears to be a ball. The question is should there also be a spring. Has any one else had a similar problem, the bike was fine all through the winter period and now I have patches all over a clean patio how annoying.

 

[FinalImpact]

Hi, I need help with the fuel tank filler cap breather system. I previously thought I had an oil leak, as there were small puddles on the ground under centre stand. Now looks like this deposit is coming from the fuel tank breather pipe. In warm weather fumes can be seen coming from the pipe, after a while the fumes seem to condense and there is an oily type substance dripping from the pipe onto the ground under. Eventually the puddle can become 4 inch in diameter. I dismantled the filler cap to check the airway through it. Now I don't know if all is well. Has anyone out there taken the filler cap apart and can give me some advice please. After removing the lock by taking out the two screws, under the lock is a round plate with 4 holes. 2 of the holes are for the fixing screws. Under the plate can be seen 2 recesses, in 1 there appears to be a ball. The question is should there also be a spring. Has any one else had a similar problem, the bike was fine all through the winter period and now I have patches all over a clean patio how annoying.

I have never hard it apart but I don't think a spring is required. In the event of tip, gravity allows the ball to seal the hole and stop (impede) fuel flow out the vent.

Is the tank rusty inside and HOW FULL IS IT when it piddles in the sun? If only when 105% full, I'd say fill it less. Reference is mine being filled while I'm on it, upright, NO centerstand, and fill to bottom of grid opening.... In the sun it does not puddle.

** IF ** If your tank is rusty inside, yours may have rusted through the steel vent line and when pressure builds it leaks.

TESTING FOR LEAKS:
Tools: Pressure bulb like nurse uses, hand held vacuum pump, OR a large syringe.

Connect pump or vacuum device to line either at tank or bottom of bike. Open the lid, using finger, PLUG the HOLE at the tank and apply low pressure/vacuum. It should NOT leak. A gauge would be handy....

IF USING VACUUM AND IT HAS A LEAK, your vacuum device MAY FILL with fuel!
IF the tank is FULL and PRESSURE is applied, you may hear bubbles escape inside the tank. Keep this to A BARE MINIMUM - FUEL VAPOR IS HIGHLY EXPLOSIVE!

Those are my thoughts. Let us know what you find.

 

[hamousher]

Thanks for the reply, it seems that this can happen at any tank fuel level. Sometimes it has been full, but equally it has registered only 2 bars on the fuel gauge and still has the same problem. Looking in the tank I can see no rust, looks real clean. I can't seem to get my head around what the ball does, thought it was some sort of valve but they usually have a spring as well. This afternoon I lifted the tank to check the pipes which have no problems. After I put the tank back I had a good blow up the breather, to pressurise it, after could here the air coming back down the breather so don't think there is a leak in the tank. Since posting I have seen similar posts where owners have fuel coming from the breather. It does seem to be the warmer weather that is causing the problem.

 

[FinalImpact]

Thanks for the reply, it seems that this can happen at any tank fuel level. Sometimes it has been full, but equally it has registered only 2 bars on the fuel gauge and still has the same problem. Looking in the tank I can see no rust, looks real clean. I can't seem to get my head around what the ball does, thought it was some sort of valve but they usually have a spring as well. This afternoon I lifted the tank to check the pipes which have no problems. After I put the tank back I had a good blow up the breather, to pressurise it, after could here the air coming back down the breather so don't think there is a leak in the tank. Since posting I have seen similar posts where owners have fuel coming from the breather. It does seem to be the warmer weather that is causing the problem.

Good info for us, knowing it leaks at all fuel levels.

With a spring option A. No Spring, option B.
A) When the vacuum in the tank is strong enough, it lifts the ball off the seat letting air in.
B) In the upright position, the ball is down and air flows around it allowing the tank to vent. Turning the lid (tank over/on its side), ball moves plugging vent.

See if you can do one the safer tests without blowing on it. A gauge really helps show its not leaking. Not sure if the oral test will pin point slow leak.