749R fuel tank breather conundrum - can you help ?

[Sharpy G]

Hi all
so, bit of a weird thing with the fuel tank breather setup on the 749R tank

details:

Corse billet cap has no breather

Tank blanking plug removed, fitted with threaded adaptor with a black plastic inline breather valve that will allow air in but not out and clear tube routed to front of fairing

with standard cap removed it leaves 2 open holes in the tank cap recess, one threaded one not (the non threaded one, I believe vented thro the standard cap via a rubber o ring and something in the cap frame)
so as I had the tank top valve open I blanked off the threaded one with a bolt and the open hole with a rubber plug

All looked good, however on a run out today, when I went to fill up with gas after around 10mins riding, when I open the twist lock cap it sprayed fuel out of it as if under pressure ?????!!!!!

same again up at Boxhill, however I only released the cap after fuel was being pushed up the pipe and the wrong way thro the valve into the pipe and down into the fairing !!!!!!!

anyone have any ideas please ?

or a diagram of the 749R race bike breather setup ?

cheers

Sharpy

[bolds]

Hi all
so, bit of a weird thing with the fuel tank breather setup on the 749R tank

details:

Corse billet cap has no breather

Tank blanking plug removed, fitted with threaded adaptor with a black plastic inline breather valve that will allow air in but not out and clear tube routed to front of fairing

with standard cap removed it leaves 2 open holes in the tank cap recess, one threaded one not (the non threaded one, I believe vented thro the standard cap via a rubber o ring and something in the cap frame)
so as I had the tank top valve open I blanked off the threaded one with a bolt and the open hole with a rubber plug

All looked good, however on a run out today, when I went to fill up with gas after around 10mins riding, when I open the twist lock cap it sprayed fuel out of it as if under pressure ?????!!!!!

same again up at Boxhill, however I only released the cap after fuel was being pushed up the pipe and the wrong way thro the valve into the pipe and down into the fairing !!!!!!!

anyone have any ideas please ?

or a diagram of the 749R race bike breather setup ?

cheers

Sharpy

Race set up

[Sharpy G]

Race set up

thanks 'bolds' what a star !!!

[KeefyB]

Sounds like the breather valve might be faulty(no.4 in pdf) or partially blocked.
Not sure about blanking off that threaded hole either,.....is'nt that part of the tank overflow system?