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Just a reminder to all you Dart owners to check for fuel tank/fuel tap leaks as part of your routine maintenance. It’s well worth the effort to take the panels off for a check- Even if you have an aluminium tank!

It’s well known that fuel tank and tap leaks are a problem on darts, and the aluminium tanks go a very long way to solving this. However if you still have an original fuel tap there are 3 common mechanisms by which leaks occur.

1) warped flange where it mounts to the tank (don’t overtighten!)

2) leak down the float tube and out the level sensor wire

3) leak out of the solenoid body due to cracking of the potting.

There isn’t much that can be done to cure these problems which potentially are worse with change in fuel composition and age, and of course new taps are not available, and not common to any other bike. There are options if you are prepared to forego the level sender although even these are very hard to find.

I had used a fuel proof epoxy to seal the very minor weep out of the float wire, and it’s held for 3 or 4 years, but during my checks before this riding season I’ve found the epoxy softened and cracked and whilst not leaking it’s definitely got fuel residue in the area, so I’ll deal with it.

Also worth while you have the panels off checking the oil cooler pipes, which can be known to split too.

Dear Tom,
Ok, thanks, good tip, I'll have a look and report back. Do you know what kind of material the original tank is made of? Is it ABS plastic?
Thank you and best regards
Matthias

Not sure what the original tanks are made of. There are no material spec markings.

What I can say is that they aren’t dimensionally stable so any repair to them needs to be a little flexible as well as fuel proof. Also, the outer surface is fairly repellant to anything bonding to it. It can of course be roughened up but below the surface seems porous.

They tend to split around the bosses for the fuel tap or the air filter hangar. Beware over tightening or using too long a bolt here.

Wise words about not over-tightening the fuel tap bolts. It's not a compression seal!
I managed to fix a persistent weep on mine by changing the O-ring (5).
I found it a bit fiddly to change, because I had to stretch the new O-ring over the float (unless there's a way to dismantle this?).
Anyway, new O-ring worked and it doesn't leak any more.

The o ring should fit quite easily over the float, however normally the float expands in use and this is probably why it was tight to get off.

Always a good idea to change the O ring when reassembling the tap. Sometimes a smear of hylomar on the flange faces is a good idea too.

You are quite lucky you managed to extract the float from the tank as usually they have expanded to the point where you can’t pull them out of the hole. If this is the case then be extremely careful as you can break the brass tube if you use too much force. It’s better to file the tank hole with a needle file until the float will pass through, but be careful as there is only so much material you can remove before the seal won’t work!

When we had the aluminium tanks made we specified the hole slightly larger to accommodate swollen floats.

Today marks possible extinction of the species for dart fuel taps- I have just fitted what might well be the last new old stock one in existance. As my 501 dart is my forever bike I was hoping I wouldn’t have to use it so soon, but we’ll see how long this one lasts.

It was particularly nerve racking for me as the standard tap orientation pointing forwards does not work for me (too close to the cylinder head which is of course taller with a 500 engine.) so I have to carefully bend the brass tube 180 degrees so I can fit the tap the other way round.