Fuel Tank breather valve info please...

[Iconic944ss]

My baby seem to be hesitating on accleration lately....

not a good opening line for a song but, it is very noticeable on some throttle openings. I have noticed at times the gas is under quite some pressure on opening the filler cap - If my reasoning is correct the little alloy breather valve in the vent hose allows the pressure to build to a set value - yes ???

Well, my bike seems to run a bit better without the valve in place. I also tried blowing down the darn thing and couldnt blow through it. I'll try with a hand pump sometime but does anyone know what the open value should be?

Also is the valve just to prevent the petrol gassing off continuously or does it have another function??

Cheers

[KeefyB]

I think the little alloy "valve" is just a union for the breather pipe.Its there so you can disconnect it to lift the tank.If it is blocked that may be the cause of your problem.

[Derek]

I posted an answer to this a couple of days ago but it seems to have got lost in the server changeover.
Anyway, the valve should have a little arrow on it pointing away from the tank. It should be possible to blow easily in to the tank direction but there should be a slight pressure required before it will blow in the outward direction. I think this is to prevent fuel surging out under braking. If you can't blow through it in any direction, it's buggered.

[Iconic944ss]

Cheers guys - I can get a flow through it but only at about 20psi - no wonder my lungs were aching !!!

Time for new one I guess.

[phillc]

Frank, I'm not sure if you remember my horror story a while ago about my tank imploding. See the pics here:

http://www.kapital-sales.co.uk/desmo/images/Tank/

And read about it here -

http://217.199.188.40/control/boards/viewthread.php?tid=3795

Final conclusion was that it was caused by bad venting of the fuel tank and quite possibly a defective vacuum pump.

I hope the same thing isn't just about to happen to you too!!

Phill

[Iconic944ss]

Cheers - dont worry - I've taken the valve out and am simply running a vented tank and losing a little gas I guess.

New one is about £20 !!!

[Iconic944ss]

New breather valve arrived today from JHP and mine was obviously poorly.

The new one begins to vent air at around 3psi so obviously there is meant to be a slight pressure in the gas tank (to help prevent it continously gassing off I guess).

SORTED !!!