Petrol has changed over the years : do you remember filling up with Leaded 4*..? We now have 95 Octane UnLeaded with there being some 97/98 Octane 'super' Petrols.
These modern Petrols are blends of classical oil industry derived Petrols and Bio-Ethanols. Something like 5% (or more) of modern Petrol has never been near an Arab..! Its bio-fuel - as mandated by the Green Lobbyists within the EU. There are also other 'chemically aggressive' additives in modern Petrols.
Unfortunately, these new additions to Petrol have a tendancy to chemically attack the rubber compounds historically used to make fuel hosing, causing them to perish, crack and weep.

It does not take a Rocket Scientist to figure out that weeping fuel lines can cause FIRES : burning your precious VW out on the roadside like so many we have seen allready.

This never used to be such a problem with mineral-oil derived petrols like Leaded 4* - these were low on naturally occuring alcohols and ethanols - being purly mineral oil based.
However, now that we have this more chemically aggressive modern petrol with bio-fuel content it has become a problem : older grades of fuel hosing that happily ran with Leaded 4* do not happily run on modern petrol - though people seemingly expect it to - their permititvity to alcohols and ethanols is so high that they perish /rot / crack / weep really quite quickly - in a matter of weeks is not uncommon.
There is a lot of anecdotal evidence to support this - especially relating to the old cloth over-braided hosing.

By way of example heres some permitivity figures I have compiled during my researching :

SAEJ30R6 fuel hosing : commonly used in the late 80s / early 90s onwards
ISO7840A1 fuel hosing : this is the grade mandated for use in Marine applications
SAEJ30R9 fuel hosing : modern fuel hose for use with bio-ethanol enriched fuels to 50% by content

Previous gradings would perform worse than the R6 shown above. Actual figures may vary between manufacturers - the above being typical figures for the class.

So : you can see that modern fuel hose that has been DESIGNED to work with modern fuels has less than 3% of the permitivity of 1980s/1990s fuel hose. It even performs better than the hosing mandated for use in the MARINE environment, where they are hugely stringent about fire-safety.!
(though saying that the Marine Grade hose has 2.1/2 minutes of self-extinguishing fire retardance should there be a fire)

Conversly, we can see that as bio-ethanol contents of modern petrols rise, older grades of fuel hosing will rot/perish/crack/weep at an increasingly quick rate from the point of installation.

Picture Courtesy of "coopersim" on the www.volkszone.com Forums

It is of EQUAL importance to select a hose with the correct inner bore diameter (I/D) as it is to select the correct hose grading.

One of the useful propertiers of rubber is that it has the ability to stretch - and to 'recoil' back to its original shape. The material essentially behaves like a mouldable Spring. This elastic spring force combined with the friction between the hose and the pipes generates 'Grip' that under normal operations will hold the hose in place (in a similar way that a rubber tyre grips the road).

The ability to stretch combined with the Grip generated is useful as this means we can get the rubber material to strech over the ends of metal pipes; providing its own seal as it 'recoils' and moulds itself to Grip the profile of the pipe. (Within the reasonable limitations of the material)

This is appropriately demonstrated in the picture below - based on the stock VW application of 5.5mm/5.6mm I/D bore hosing onto the 6mm O/D metal stand pipes of the fuel delivery system.

Volkswagens Engineers thought that the Grip of the rubber on the fuel delivery pipes was sufficient on its own to provide a reliable seal : hence stock VWs not having any fuel hose clips on the connections as they left the factory.

An ideal clamp will generate a UNIFORM clamping force around the hose, with this evenly applied force helping the hose to form a nice tight seal.

It is important to choose and use hose clamps properly. Hose clamps are sized to fit specific diamters of hose and should only be used for those hose sizes.
Inappropriatley sized clamps will not perform as specified and will apply force around the hose unevenly.

There is an URBAN MYTH (man down the Pub rumour) that worm and band clamps 'ovalise' when tightened so should not be used on Fuel Hoses. This myth is almost certainly based on people using inappropriately sized clamps.

We can support this by comparing the 'Spider' diagrams of clamping force below : to the left is an IDEAL distribution : to the right is the MEASURED distribution from a Worm and Band clamp being used properly...data courtesy of Norma Group.

As can be seen above, Worm and Band clamps provide a clamping force distribution that is as evenly as physically possible given the Laws of Physics that determine such things.

Another fact that de-bunks the Urban Myth about Worm and Band clamps is the use of HI-GRIP STAINLESS hose 'Worm and Band' clips in marine applications throughout the world. They are manufactured to BS5315, have BSI KITEMARK and N.A.T.O. approvals and hold Lloyd's Shipping Register Type Approval for applications in the marine, offshore and industrial markets.
If the 'ovalisation' problem was inherant in the design then they would not have gained the above approvals.

A good rule of thumb for worm and band clamps is to have approximately 1/8" (3-4mm) of band protruding beyond the worm drive when the clamp is fully tightened.

There is an alternative to Worm and Band Clamps - Captive Nut and Screw clamps - most of the top clamp manufacturers make them in addition to the Worm and Band Close. Often referred to as 'Fuel Hose Clips' : though they can be used to clip any hose - in much the same way as a Worm and Band clip.

A good feature of the Captive-nut and bolt clips is that they often come in a more extensive set of sizes, especially for fuel hose sizes, than Worm and band clamps. The ABA range stocked by Volksbolts Ltd. moves up in 1mm Diamter increments.

Clamps should be torqued properly to assure proper seal - for Captive Nut and Screw & Worm and BandClamps through size #6, use 25-30 inch pounds; for Original Clamps sizes #8 through #16, use 30-40 inch pounds and for sizes #20 and higher, tighten to 40-45 inch pounds.

With the increasing aging and wear & tear taking its toll on Air-Cooled VW designs people are increasingly encountering age related issues.

One issue of specific concern is the wear & on the metal inlet / outlet pipes on the Stock VW fuel pumps and Carburettors : These were simply pressed into place at the factory that made them.

As can be seen in the below photograph : these press-fit parts can work loose and seperate from the carburettors / fuel pumps.

Picture Courtesy of Venomous Werks - Classic Volkswagen Specialist

If this happens on a running engine the results could be catastrophic : regardless of whether you have used the correct fuel hose and clips.

To check simply give the pipes a 'wriggle' : any signs of looseness will make themselves apparent quite readily.

Repair advice given out over the Internet for this problem varies but can be summarised as below :

• Replace the entire fuel pump or carburettor with a new unit.
• Peen the aluminium casting around where the brass pipe enters the casting such that the aluminiumn deforms and clamps the pipe.
• Use safety wire to anchor the adjacent hose clip to the body of the fuel-pump / carburettor.
• Refit the metal pipe fitting using a strong loctite or equivalent.
• Tap the 6mm hose to take a screw-threaded fuel hose fitting of appropriate size.