Tank Breather Blocked

As far as I know it just vents into the top of the tank. You should be able to see it with a mirror in the filler cap. If you take the filler assembly out you may be able to get a hand onto it.

 

It is just a stub pipe welded (or brazed) in the top of the bulge.........Try pushing a piece of 3mm / 4mm strimmer line in from the outside........cut the line with a knife so you get a pointy angle on the end.

 

I think the plate may be a baffle of sorts, so if you can get above it from inside you may find the outlet, although I doubt that will help you.

The stub pipe on the tank is 2 way.......ie: without the valve in place, petrol will p*ss out of it easily.

The silver valve has a small arrow on it which faces forward (away from the tank)......they can become faulty, but don't always think that it is.

It should let air into the tank easily (in the opposite direction to the arrow) but it retains some resistance in the direction of the arrow untl it reaches about 4psi (which is stop fuel from p*ssing out); a pressure which is variable in my experience.

This is because if you top your tank up without brimming it and let the bike stand you may find the valve won't blow to let the fumes and pressure out.

This in turn, with the heat of the engine and the petcock left open, it can pressurise the fuel lines, force the float needles open and not only does it start running out of the carb overflows, you could lose a lot of fuel because a siphon effect occurs.

If you try cleaning the valve, only use carb cleaner and shake the excess out.

A 2mm brake cable may not have the stiffness to cut through the POR 15 and, more importantly a build up of rust and paint which has already partially blocked the stub pipe, particularly if you didn't clear the breather before you applied the POR 15.............It took me quite a while to clear paint out of the stub on mine.......and that is without POR 15.

 

I reckon that's asking for a small hole in the top of the tank......I would persevere going in from the outlet end of the stub pipe.

How far down the stub pipe will anything go before it stops?

If there is a lot of cr*p stuck in the pipe, you could try hand turning a 3mm - 4mm drill bit in it from the outside to try to pull some of it out.

 

I have the same issue... Simon, how did yoy resolve it please??

 

I had the same problem, after a couple of miles the engine would cut out caused by the vacuum created by lack of venting in the tank.
I had my tank repaired, repainted and internally coated by the mechanics at Ducati Mcr.
After many failed attempts by myself to clear the blocked vent pipe I took it back to them and they managed to clear it.

 

From the outside??????!!!!!

 

So, four hours later, a mirror, a torch, a 90 degree dental tool and an endoscope plus hand manipulation a gynaecologist would have been proud of... it is all sorted. The inside vent hole is on the bottom of the raised area opposite side to the external vent tube about 2cm from the edge.

 

Good lad, well done!

 

My grandma’s saying.