fuel leak su carburettor

[cococola]

I have noticed today that I have fuel leaking from the side of my su carburettor and on close inspection underneath the fuel in point, there is an alluminium tag, under the tag is a small hole (breather??) and the fuel is from there.
What is the relevance of this hole and why is it leaking please?

[bmcecosse]

The float valve is passing and the float chamber is overfilling... What pump are you using - a normal Minor SU electric pump?

[cococola]

yes normal electric pump

[bmcecosse]

Float valve then - unless the float is punctured - but that's v unlikely with the plastic float.

[kennatt]

Sometimes just taking top off the carb,and blowing through the inlet can clear the valve of any grit,but a new valve assembly is inexpensive and relatively easy to change,just remember that the carb is above the exhaust,and petrol running out of it is not a good idea

[cococola]

Ive took the top off and blew through the nozzle and refitted.It weeped after about 5 minutes running so I tapped the body and restarted the car and it is now dry so I suspect the valve was maybe sticking?

[mogbob]

It's good that you have confirmed the problem but.....follow kennatt's sage advice and replace the valve assembly asap !!

If you continue running the car " as is " and the next time it decides to stick again, is when the engine exhaust is hot, then
you will have a real problem.Aside from personal ( and passenger ) injury, scary enough, you will have a burnt out wreck.
Nobody wishes that on anyone.Spend a few pounds for safety's sake.

Bob

[kennatt]

Yes tapping usually makes the valve open or close,but it may well stick open or shut again,its usually caused by slight wear,or grit ,it can be sometimes cured(if you are desperate) by lapping it in with valve grinding paste,put a dab on and twist the needle back and forth.make sure its well washed out with petrol afterward. But I would just get a new assembly,and forget about it for the next 20 years.May be worth having a look at the filter in the fuel pump to make sure ,It has one and that its not damaged,thus letting crap through from the tank.

[bmcecosse]

It wears into a ridge - so I would just get a new one rather than 'lapping'..

[cococola]

I will certainly get a new one.On Ebay they seem to be £14 inc postage

[cococola]

I fitted the new valve and it remained dry for 5 minutes ...then fuel leaked again.
I know the fuelpump is correct su pump and the only other thing that I did was replace the fuel pipe from the pump to the carb.The new pipe is the plastic type rather than the old rubber type that was previously fitted (weather that makes a difference) I also note that on research there is a suggestion of correct float level adjustment...Ive never had cause to remove the carb top previously so can the float go out of adjustment at all? Also how do I check and adjust if needed please?
Sorry for all of the questions.

[philthehill]

You say you have the right SU fuel pump - are you certain you have the right fuel pump?
Even though SU fuel pumps can look the same they are different and can be high pressure (HP) and low pressure (LP).
There should be a tag on the fuel pump which states the fuel pump type for example - AUA25 (948cc) or AUA66 (1098cc) and are both LP pumps and which gives a line pressure of about 1.5 lb/in2.
What are the letters/numbers on the tag fitted to your electric fuel pump?
HP pumps will give up to twice that pressure 3.0 lb/in2 and may overcome the float chamber valve.
See BMC wksp manual section BBB.4 for setting the fuel level in the float chamber.[frame][/frame]

[cococola]

My pump says AUA66 on the side tab and part number 4080 on the bottom

[philthehill]

You have the right SU fuel pump if your engine is a 1098cc unit and fitted with a HS2 carb.
Therefore I would check the fuel float chamber valve setting as per the wksp manual details above and below if you do not have access to a manual.[frame][/frame]

[cococola]

Fabulous info thank you Ive had the top off the float chamber today and the float level was out so I reset it as per instructions and ran the car up fand it was dry for about 20 minutes which is more than before...then the fuel leaked again

[Trickydicky]

If fuel is leaking from the breather hole it can only be down to one of two things, either the float is punctured or the needle valve is set incorrectly. Are you sure the leak is from overflow hole?
Another thing to check is the stub pipe attached to the carb top, is it deformed in any way and allowing fuel to creep past the pipe?

[cococola]

The leak is certainly from the overflow hole.With regards to settling the needle valve I replaced the old one in the chamber lid and screwed in the needle body till tight and then put the inner needle inside..Is there an adjustment on the needle or is it just through the float bar adjustment please?
The float is all ok with no punctures.

[mogbob]

It's just the float level adjustment that's available to you.
However, if after further adjustment it still leaks then the previous suggestion( Trickydicky ) of the supply pipe leak ( probably through the rubber perishing / clip not tight / distorted ) must be investigated.
Bob

[cococola]

Ive replaced the fuel pipe with new as it didn't look great but the leak is still there.I wonder if I adjust the float even more than the recommended adjustment may help?

[bmcecosse]

The HS2 pump float level is basically 'non-adjustable' . Take care not to damage the float if you do make any adjustments.