fuel tank vacuum...

[RobC]

Can anyone help?

I'm getting a massive hiss from tank when I open petrol cap when I've been out for a drive, also got a slight hesitation when accelerating and not all the time only when warm. Anyone suffered this before and how to over come it...?

I've had the breather off the tank and cleaned it... (tis a ball bearing type) this has no pipe attached, should this have one attached to it?

Would be handy to know what others with similar tanks have done...

Also replaced plugs and leads with new... no change

['Mendip Wurzel']

I've just got an open vent pipe that goes up above the tank and back down with a smaller hole in the end and facing to the rear. There is also a tap to totally close things off in the winter.

If the hiss is air coming out of the tank under pressure than I would guess not so much of a problem. If it is sucking air into the tank then not ideal.

[RobC]

this is something I need to determin. with a bit of paper

All I know for sure is that when I had her recently set up .. the rear was in the sun... the tank had warmed up and the fuel in there had expanded and the breather was hissing...  which I have never heard before...

It's my understanding that the breather on the tank is open to air unless I roll it and the ball bearing seals the system/tank to stop fuel leaking everywhere...

['Mendip Wurzel']

I think am illegal without a fuel vent, however I have heard that the ball bearing type do have a limited life, like maybe changing every few years though I'm no expert on this subject. I never use my car on the track and I have had plenty of fuel starvation problems in the past so I didn't want another thing that could go wrong. 

It always interested me that Rimmer Bros sold their fuel filter as a fuel vent/filter. I was thinking of maybe using one of these as there is less chance of it blocking and minimal restrictions for more air flow.... maybe I am talking rubbish here.  See following link...

http://www.rimmerbros.co.uk/Item--i-GFE7004

The other thing that worried me about a blocked vent was is there sufficient suction to crush a SS tank, which could be costly. This certainly happens with outboard motor fuel tanks if you don't open the breather vent.

Also, you need to allow air out of the tank in warm weather, which a one way value may not do and could put pressure in the system with possible problems like petrol being forced out of the carb.. 

This is why I thought ... forget it.

There are things that let air in and out, but don't let fuel out with a little float thing that you need to mount vertical but this was getting too complicated and costly for me.

[RobC]

cheers fella...

Not had time to go out in her yet... but I've rigged up an open piped vent. To see if this solves the problem. Fingers crossed

['The Gaffer']

You might just want too check the small section of ali tube into the tank for a blockage.