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MG Midget and Sprite Technical - leaky fuel filler ?

I filled the midget right up to the brim the other day, and noticed a day or so later a whiff of petrol in the boot. I dont normally fill it so full, and have noticed any petrol smells before.

There is no obvious signs of any leaks, and once the fuel level dropped a bit the smell went away.

I had the tank out last year and pressure tested and it was ok.

So I'm guessing there is either a slight leak at either end of the filler, or maybe the pipe is old and porous ? I'm guessing the pipe needs replacing eventually as the rubber degrades ?

That would be my place to start, especially if you're using petrol containing ethanol.
As it happened when the tank was full, another possible culprit is the gasket on the sender unit, which is a PITA to check.
Jeremy MkIII

Is it the original rubber filler connector hose--
Back in the mid 80's here when unleaded petrol was first introduced, there was a recall on the Ford Falcon station wagons for a fuel smell issue
The wagons have the fuel tank inside the car and it was found that the filler neck hose, which was the same hose as previous models allowed fumes from the unleaded fuel to enter the cab--something that hadn't happened previously with leaded fuel
The fix was a new silicone based hose instead of the reinforced rubber one
William Revit

The addition of ethanol also has an effect. My pal's Morgan Plus 4 has gone through 2 rubber filler necks and its only a 2007 model. Morgan have said there is little they can do about it as the design has remained like that for many years and previously there had been no problems. No help when all the fuel spews out at the filling station!
Bob Beaumont

Yes its the original (rubber?) fuel filler pipe as far as I can tell.

As part of my pressure testing, I noticed a leak around the sender unit. i fitted a new ring and gasket and the tank held pressure. So it should be good, although it could have started leaking again I suppose.

On the Falcon's it wasn't a visible leak, just the fumes wept through the rubber
William Revit

ISTR smearing a little polyurethane sealer on the tube to try and get a good seal.
I generally try to only fill to the bottom of the tube - but it does overfill sometimes, so need a good blast to use up a bit of fuel asap !!
richard b

ISTR a difference in appearance between the 1500 hose and earlier models.

Apart from the obvious differences in shape and length, due to the reinforcements in the boot of the 1500, the earlier hose has a shiny rubber appearance and the 1500 seems to have a woven outer cover.
Dave O'Neill 2

have you forgot my mate's loan of a new sender spanner set.

IF your rubber filler hose in the boot is original DO NOT replace it, you'll probably get more modern piss-poor.

As a general rule unless you really have to don't risk buying piss-poor modern rubber.

Petrol expands and creeps (yes I know those are not the right words but you know what I mean) in the heat - which is why you should fill up when it's cool to get more for your money but you must allow for the 'expansion' of a hot day.

If you can spare more petrol, say from your spare can, fill until you can see the petrol in the filler neck - careful is very clear stuff when poured slowly.

Then look to see where it leaks.

It the sender or tank is leaking you should see the petrol carrying the muck or cleaning it off, takes Waxoyl off very well.

If you can only smell it then you like me should have used a sender spanner to fit the sender - or possibly the seal is piss-poor rubber. I might add some sealer with the new (possibly piss-poor rubber) seal as Rich mentioned, don't know what it is as my mate is giving it to me.

I normally fill to the back of the petrol cap as I only have a modern 5.83gal (25.5l) tank.

Nigel Atkins

ETA: sorry I've had too much sun, that post had too many errors to beat the edit guillotine -

... careful [petrol] is very clear stuff when poured slowly [you could have it spilling from the filler over you paint].

... If you can only smell it then [perhaps] you, like me, should have used a sender spanner to fit the sender [last time] ...

Nigel Atkins

more thoughts -

I didn't mean to dismiss the idea of fmes getting through the rubber rather than liquid but if it's just because of overfill and pressuring up from the hot weather that causes the fumes through the rubber then I'd keep the rubber and fill less when hot.

Is your petrol cap venting, the seal gone, a thing they checked at MoT(?).

Do those old SU fuel pumps vent/breather into the boot(?)( I can't remember).

A whiff of petrol at the rear isn't always easy to track - on a NEC ride I thought there's a strong of petrol from the rear and it turned out to be Williams Waterless overloaded microfibre cloths in the boot! :)
Nigel Atkins

“Do those old SU fuel pumps vent/breather into the boot(?)( I can't remember).”

Doesn’t Chris have a 1500?
Dave O'Neill 2

Yes of course - it has been a very hot day and my brain was pre-frazzled.
Nigel Atkins

Nigel the fuel cap is new, and a vented type.

The tank has just the one feed to the carbs, and a vented cap, nice and simple.


yes, I forgot the 1500 fuel pump, far too hot for me now - but - new cap, it's new so does it work? :)

I'd hold off until this heat has gone to further investigate for leaks to see what difference this makes and how much it needs chasing up.

I expect you've covered the simple and obvious like checking tightness of 'jubilee' clips, spillage or fumes from petrol can to other items in boot.
Nigel Atkins

Chris, sorry if I'm labouring the bleeding obvious, but...
Have you only noticed the fuel smell since getting a new fuel cap?
If it's not venting adequately might it find a way to vent vapour into the boot?

I'm sure I've seen blue silicon fuel filler hose specific to the 1500 being sold by someone or other, but don't remember exactly who. I seem to recall idly pondering if I should buy one, but there's nothing wrong with the one in the car, so I got over it.

Greybeard no I have had the new fuel cap for about a year and the car has been running fine. The fuel smell I noticed was last week and I think coincided with filling the car right up to the brim.

I filled up last night with the fuel nozzle all the way in and stopped refueling at the automatic cutout. I then drove the 30 miles home so the fuel level should be below the filler pipe now. I'll check the boot tonight but I suspect there wont be any smell.

The next check will be to fill up to the brim again and leave it over night.....


On my 1275 with the nozzle pushed fully against the filler tube neck the auto cut-out seems to stop before the tank is full let alone the filler neck as I seem to get much more petrol in before the second and third auto cut-off, can't remember how much though. That's before I rest the nozzle on the neck opening and watch the petrol gulg up towards overspilling before settling back down and I do that a few times until I can see the petrol level with the top of the filler neck.

If it's hot I have to drive as quick as I can to save wasting the fuel.

Same with if I'm running out of petrol in the tank I drive as quick as I can to get to the filling station before I run out, still not able to convince my wife of this.
Nigel Atkins

Nigel said " the auto cut-out seems to stop before the tank is full let alone the filler neck as I seem to get much more petrol in before the second and third auto cut-off"
Exactly the same thing happens on the MGB. I think it's something to do with the tank being a flat shallow box. Air gets trapped without the tank being completely full. I actually rock my BGT by shoving against the left hand rear wing and that seems to encourage the air to escape and another gallon will then go in.
Mike Howlett

Mike, I think you just need to risk your health and towards the end of the fill have the petrol pump nozzle seal away from the filler neck opening (losing all those petrol fumes you're going to pay for). I've had cars with upright tanks and still had problems filling the last bits even when the filler neck openings have been very large.

The problem is to have the light to see when the petrol is about to flow back over your paintwork.
Nigel Atkins

I'd put money on the sender gasket. I had just that problem but it only showed if i jacked up the back end and fuel ran off the top of the tank.Just a rotten job to do because you have to run the fuel down sufficiently to drop the tank. In my case the gasket was ok (but I did change it) but the screws were not sufficiently tight. I also discovered a punctured float half full of fuel.
Graeme Williams

Chris fitted a new gasket seal last year and on our tanks these are rubber, or is it plastic, rather than cork, I can't imagine for a second that a new rubber seal would go faulty, if it did it would be because they were fitted incorrectly - or of course it's the efanole wots dun it.
Nigel Atkins

It still sounds like you are getting fumes through the filler neck rubber to me, which I mentioned early on
If you can't get a good silicone hose for it, if you go to a place that sells turbos they will have plenty of nice reinforced silicone hose---you need the silicone hose, or silicone lined hose, if you're using unleaded fuel
William Revit

This thread was discussed between 23/07/2019 and 26/07/2019

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