Carbs....leaking?

[Alex]

My 2000 has HS6 carbs, it also is thirstier than something very thirsty.
I keep getting a smell of fuel when its sat not being used,this smell is at the front of the car.
If I put my head/nose near the front drivers wheel its strongest and if I look at the chassis rail under the carbs its plain to see why.
I cant find any obvious leaks however the airbox often has fuel in it.
I've been advised that its possibly the needle valves not closing off and allowing the floats to rise.

Heres the odd bit( i think?)....
If I park the car up with for example 1/2 a tank of fuel next time I use it its between 1/2 and 1/4.
This makes me wonder if it could be leaking from another point.....but surely it would only drain the float chambers?
Or can it drain the system slowly somehow?
I'm under strict instructions not to spend money on the car at the moment so wondered what people thought?
Still needle valves?

On another point.....if I wanted/was allowed to buy an overhaul kit how would I know what model HS6's I had?
I dont have a clue what they started life in and the dont seem to have a tag on them......

Thanks
Alex

[Richard B]

Alex wrote:

.....but surely it would only drain the float chambers?
Or can it drain the system slowly somehow?

Syphoning....  :-/

[Alex]

Ah thats the word I was looking for ;D
Do you maen is someone syphoning it off?.....easy answer no,not where we live ;)

[Richard B]

No I mean syphoning from the tank through the pump and carbs until the fuel level in the tank is below the point of leak.

Could be the O rings between the resevoir and the jet of the SU's

[Alex]

Sounds like you could be right Richard.....it always seems to settle at about 1/4 ....

O rings between the resevoir and the jet of the SU's .....elaborate please :)
Where do I get some, ;D how do I change them etc etc etc

[thebrookster]

Alex, you should have a smal tag attached to one of the screws of each float chamber on each carb. This will have stamped on it 3 digits, then 3 numbers, then either R, C or F (depending on no of carbs, these simply stand for Rear, Centre and Front; a twin carb setup will only have R and F). This designates what type of carb it is. Do a google search for SU carbs, I use a guy called Andrew Turner (in fact I just bought a rebuild kit of him today for my carbs!!) at http://www.su-carbs.co.uk/ who is very knowledgeable and extremely helpful. He will quite willingly sell you a rebuild kit, service kit or refurb your carbs for you!!

If you do not have the tag then maybe someone else on here can tell what you have?? Else I personally would just send the carbs to Andrew Turner and let him do the guess work  ;D ;D ;D ;D ;D

Hope this helps,

Phil

P.S A rebuild kit for my spitfire HS2 carbs came to approx £50 just to give you an idea of cost on that front.

[Alex]

No tags on my carbs :(
Cant afford to pay Andrew Turner to repair them, my car is a toy that with 2 kids I struggle to justify to SWMBO.
I need a nice cheap fix idealy.....

[Lord Sorbington]

You'd probably get away with a seal and gasket kit, mine cost about £10 from Chris Witor.  Petrol smell and leaks cured.

[Nick Jones]

Alex,

If it's getting into the airbox then it can only come in through the jets - which means that the fuel level in the float chambers is high enough to allow it to overflow the jet tops.

If it does this for a short period when switched off then it could just be float level too high or fuel pressure too high (will lead to rough, rich and dying off idle if bad enough).

However, if it keeps on doing it slowly, over a long period and it is coming through into the airbox it has to be slowly leaking through the needle valves, syphoning all the way from the tank and then overflowing through the jet into the throat of the carb.

This could be caused by the needle valve itself leaking or possibly due to leaking where the needle valve screws into the float chamber top.  There should be soft aluminium washer there which seal the joint and are used in different thicknesses to set the float height.  Suggest buying new needle valves (can get viton tipped ones which are supposed to seal better) and a selection of washers so that you can set the float height correctly.

It's also worth being aware that SU twins can sometimes have different float chambers and chamber mounting rubbers and spacers on the front and rear carbs.  This is because where their installations are angled and the front carb has the float chamber at the front and the rear at the rear, the installation angle causes different fuel levels in the jets if the carbs are the same (if the engine is tilted downwards towards tjhe rear, the front carb would run richer as a result).  Mixing and matching parts from random SUs can sometimes has unexpected consequences as a result.

A set of AT fettled carbs might pay for themselves quite quickly at todays fuel prices......

Nick

[Alex]

Thanks Nick, looks like I need to get some needle valves then.
Really hoping this solves my cars thirst as it's what prevents me using it alot more.

Alex

[Alex]

I see they do small bore and large bore needle valves.....how do I know what I have?

[Nick Jones]

Errr..... I thought the HS6s had the larger ones but a bit of googling suggests the HS6 is in fact the only size that both needle valve sizes were used on (typical!).

Can't find my SU box just now - will have proper look tomorrow if you are still stuck.

Nick

[Alex]

Thanks Nick :)

[James]

I had to fit large needle valves to my HS6s, I used the all brass ones. No issues with them after that.

[Alex]

Any idea how you know which you should have though James?

[James]

No idea, mine were big ones meant for a Jag.

They worked fine though I did also have a pressure regulator.

[Glenn]

Richard B wrote:

Could be the O rings between the resevoir and the jet of the SU's

This has been the cause of a few leaks I've had on different SUs.  Where the flexi pipe of the jet meets the float bowl, this can be a dodgy seal.  If you run your finger up the jet pipe, you'll feel if there's a leak.  Inside the connection there's a brass washer which can get lost and a flat section black o-ring which goes hard.  Both are cheap from Burlen.  If that doesn't do it, a new jet'll sort it out.

I have had dodgy needle values, but for me that has made the fuel leak through the gasket on the float tops.  If you think they aren't sealing, you could always try giving them a clean up with your airline first and see if that improves them?

[Nick Jones]

Haynes SU book does not cross reference needle valves sizes with carb type or application.....

I suspect they will be interchangeable and large ones will be needed for more powerful engines (depends how optimistic you are feeling  :P).  Suggest you ring Andrew Turner or Burlen.

Cheers

Nick

[Alex]

I just inspected my needle valves....they have a very slight lip that I can just feel with my nail.
Theres a shiny ring where they have been fitted.
Is this normal or are they shot?

The fuel level doesnt seem very high inside the float chambers, however the fuel level in the tank is now down and I dont want to top it up just so it can leak over night.

If the marks on the valve indicate that theyre knackered perhaps I've found my problems?

[Nick Jones]

Yes, that's a wear mark - they are knackered.  Should be a smooth cone.  Can also get Viton (rubber) tipped ones.

Nick

[Alex]

Thanks Nick