Fuel-air Bomb

Fuel-air Bomb

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Discussion

mphillips27

Original Poster:

7 posts

267 months

Tuesday 26th March 2002
quotequote all
Hi All,

After taking my recently aquired (wife's actually) Chim 400 for a blat around the twisty bits of South-east England this weekend, I've noted down a couple of "features" that will need adressing. The first of which is the pressurising of the fuel tank to what seems to be a least a bar or two of pressure. I'm new at this, but don't believe that having vapour rich air whooshing out of the fuel tank every time I loosen the cap at the petrol station is a good sign.

Is there a breather pipe or carbon canister I should be looking at? And if so, where do I find it? (It's a facelifted car on an S plate). I'd appreciate some advice, as It's making me nervous.

Apart from that niggle, it's the finest experience I've ever had on four wheels, and It may take some time to take the smile off my face (assuming I don't explode in a bright yellow ball of flame anytime soon)

hughjayteens

2,029 posts

269 months

Tuesday 26th March 2002
quotequote all
My tank seems to make a loud clunk after startup - I assume this is when it is pressurising??

Does that sound like a blocked breather?

mphillips27

Original Poster:

7 posts

267 months

Tuesday 26th March 2002
quotequote all
I get that too. A bit scary the first few times it happened. I get the feeling that the fuel tank is inflating like a balloon. Do you get the rush of air coming out of the tank when you take the filler cap off?

ATG

20,616 posts

273 months

Tuesday 26th March 2002
quotequote all
Are you sure it isn't de-pressurising??? Pump pumps fuel out of the tank leaving a partial vacuum unless air is drawn back in through the breather. It is often reported that the carbon filter wotsit in the breather picks up water leading to increased resistance and a harder vacuum in the tank.

mphillips27

Original Poster:

7 posts

267 months

Tuesday 26th March 2002
quotequote all
Quite sure. I thought the noise was caused by a partial vaccuum at first as you describe, but then felt (and smelled) the petrol vapour whistling past my fingertips.

beljames

285 posts

268 months

Tuesday 26th March 2002
quotequote all
My fuel tank used to go off like a gun every 5-10 minutes and it scared the bejeezers out of me, especially when sitting in traffic. This is caused by a build up in pressure that can't ventilate. Whilst the tank is unlikely to spectacularly explode the constant movement in the tank sides may eventually (and I imagine it will take a while) loosen the internal tank baffles, which would then rattle around.

Basically the car vents the petrol tank by running a pipe from the tank, down the passenger side of the car, across the front and into a carbon cannister. You will probably also see a feed from the engine, which I guess captures unburnt fumes and returns them to the tank. Finally there is what seems to be a condensate drain from the cannister channelled down through the front spoiler to the road. Through this arrangement - the whole thing 'breathes'. It is possible that either the pipe from back to front is kinked, or the cannister is blocked.

What follows is a desperate bodge (motivated by the cost of a new cannister) and is not recommended. I disconnected the tank and engine tubes from the cannister, attached a footpump to the condensate tube, covered up both the input holes, gave it two pumps (creating a small pressure vessel in the cannister) and then uncovered the engine tube input hole. Petrol shot out the cannister. I did this until petrol stopped shooting out the cannister. I then blew hard up the tank return pipe (surprising amount of backpressure!) and then sucked a bit for good measure until I fainted.

When I came around I connected it all back together and problem was solved. No more loud boinging. Needless to say - this is not a recommended TVR repair...

JB




>> Edited by beljames on Tuesday 26th March 19:02

ChrisCh

48 posts

266 months

Tuesday 26th March 2002
quotequote all
Not much to do with the thread, other than fuel is involved.
Being new to the group, can anyone advise if getting fuel into the tank is so much of a work of art as I seem to be making it. I seem to pull into the fuel station & spend many minutes with the trigger barely on on the pump, any attempt to "rush" fuel into the tank, just cuts the pump off.
Thanks in advance for any info

ATG

20,616 posts

273 months

Tuesday 26th March 2002
quotequote all

[innuendo mode off]
ChrisCh ... no exactly what you mean. I only recently learned from someone else on this site that it is possible to get the nozzle a lot further into the hole, after which you can put the fuel in at a decent rate without either half of it blowing back out, or triggering the pumps cut off.

It's awkward but if you hold the nozzle so the handle is almost bashing the underside of the bootlid and jiggle the nozzle as you shove it down, it'll suddenly clonk and slide in further. You have to wrestle a bit to get it out afterwards.
[/innuendo mode off]

squirrelz

1,186 posts

272 months

Tuesday 26th March 2002
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If you've got the nozzle fully in, you can squeeze the trigger fully open and not have it cutting out (until it's full).

If you are standing behind the car, put the nozzle in, in line with the car, then rotate the top of the nozzle section away from you in a vertical plane(difficult to describe!), and push down. It's a squeeze to do without banging your fingers on the bootlid, but you should feel it go fully in.

Can't think of a better way of describing it than that, sorry...

MikeyT

16,572 posts

272 months

Tuesday 26th March 2002
quotequote all
I've had the big loud bang from the back as well. Anout 10/20 seconds after start up.

Thought it may have been something to do with the petrol tank and pressure but wasn't sure.

James, you can do mine for me when I come over!

No naked flames tho'

mphillips27

Original Poster:

7 posts

267 months

Tuesday 26th March 2002
quotequote all
It seems a common problem. There is a knack to it apparently (which I haven't discovered yet).

quote:

can anyone advise if getting fuel into the tank is so much of a work of art as I seem to be making it. Thanks in advance for any info



Have you had the "small river of fuel dribbling down the side of the boot seal" feature too?

I was absentmindedly filling up the Chimp at a service station near Heathrow on Saturday morning. When I noticed a little splashing of petrol around the filler cap.

I felt the hair on the back of my neck stand on end when I watched this little trickle make its way down the back of the boot and then vapourise on the hot exhaust. For a few seconds I waited for my life to begin flashing before my eyes, and then realised that I should probably find a paper towel, and maybe some clean underwear.

mphillips27

Original Poster:

7 posts

267 months

Tuesday 26th March 2002
quotequote all
Thanks for the tip JB. I'll try it at the weekend

quote:

Whilst the tank is unlikely to spectacularly explode the constant movement in the tank sides may eventually (and I imagine it will take a while) loosen the internal tank baffles, which would then rattle around.




Agree, but I would hate to be in a serious prang and have the tank split. (Barbeque anyone??)

ChrisCh

48 posts

266 months

Tuesday 26th March 2002
quotequote all
Thanks for the info on spending less time at the filling station, if you have read the other messages tonight, you will know what I mean when I say that I will try the suggestions when I have 4 wheels on the car!

Chris