what are these tanks for?

[rustydubber]

Hi,tank each side under rear of front wheel arches,pipes running off them looks like they go to fuel tank,

[HarryMann]

Overflow/breather tanks for the main fuel tank...

[rustydubber]

Thanks for that

[dansimpson]

What would happen if these tanks were removed? Given tha they seem to cause a few problems, has anyone tried an alternative location or method of acheiving breather/overflow sysytem?
Dan

[CovKid]

These tanks provide expansion room for the air/gas in the main tank and are mounted higher to aid with that. I'm not aware of any problems with them beyond 25+ years of hose deterioration or some clot drilling into them from above the wheel arch. They do the job and with a set of new hoses will continue to work well, probably for another 20 years.

Mind you, try removing them and plugging the vent hoses from tank and you'll discover that filling becomes a completely frustrating if not impossible operation. In another thread I compared this to putting a hose on a tap and connecting the other end to a bottle. If you turn the tap on, the air pressure in the bottle would rise rapidly and no more water would be able to get in. All that would happen is that the pressure would blow the hose off the tap. A fuel system needs to be sufficiently sealed to minimise the risk of fire but by the same token it can't be totally sealed as either fuel wouldn't flow or the changes in pressure within the system would cause the tank (or the weakest part of the chain) to distort. This is what the expansion tanks do. An additional feature is the tank return pipe. If the expansion tanks are not working due to blockage or damage, you'll only be able to get small amounts of petrol in the tank at a time or it will spit back through the filler.

I imagine there are other ways to achieve a similar result to that provided by these expansion tanks but can't see its worth the bother to be honest. They work perfectly if its all in good order. A choice phrase here would be "Don't over-egg the pudding".