leaking carburettor

[bootlid]

Dear members,when i purchased my series mm lowlight recently it had a bad petrol leak from the securing nut which holds on the float chamber bowl,i purhased a complete set of new gaskets/seals and had the whole carburettor old ones replaced by a experienced person,guess what ?,it still leaks,does anyone have a clue whats wrong here.

[taupe]

Could be a split in the securing nut?

[bmcecosse]

Fuel level too high......

[bootlid]

Would that mean a new lid,i,ve priced one at burlem,£48, a bit dear but exploring all possibilities,thanks for reply.

[bmcecosse]

New lid? 48 Pds !!!!! Check the float is not leaking - and then set the level. Also check the float valve isn't leaking.

[mike.perry]

Have you removed the air silencer so that you can see inside the carb?
Is the fuel dripping out of the throat?
Is it dripping from the bottom of the float bowl?
Can you move the float bowl?
Are the washers fitted in the correct order?
Do you have an exploded diagram of the H1 carb?

[bootlid]

Have checked the float level,float etc,etc,all ok,petrol leaking from float bowl securing nut,all gaskets have been checked and fitted according to burlem diagram issued with new gasket/seals etc,has been suggested that worn needle valve in lid could be the problem but burlem want £48 for new lid,very expensive for mm carb,most other cars not so expensive.

[mike.perry]

There are instructions in workshop manual for setting the needle valve. If needle valve was leaking fuel would flow over the float chamber. You can check this by depressing the pin on top of the float chamber lid.
Also check valve is not leaking by disconnecting fuel pump, removing float chamber lid and holding valve closed whilst touching fuel pump feed wire against terminal.
I may have a spare needle valve.

[bmcecosse]

It is wrongly assembled jet assembly/float bowl mount. Try again!

[bootlid]

been suggested that rubber grommits on bowl assembly,not on mine,according to burlem diagram ,two fibre washers with an aluminium washer between,still leaking.

[katy]

Shouldn't be leaking unless it's overfilling unless there is a hairline crack in the top housing.

[bootlid]

apparently,there are different washers applied to the securing bolt for the float bowl depending on the carb type,it is possible someone has fitted incorrect ones to my series mm lowlight one.

[bmcecosse]

I thought you had renewed them ?

[bootlid]

yes i had ,but the diagram supplied by burlem was incorrect for my carb,it appears different rubber washers are to be tried tomorrow,so wait and see.

[bmcecosse]

Don't think H1 has rubber washers in there...... It's a simple assembly - surely must be obvious where fuel can leak ?

[Dean]

Are all the mating faces/surfaces flat and clean, all burrs removed? Aluminium parts can bruise quite easily causing parts to sit raised and in this case leak.

[bootlid]

still unable to stop leak,no visible signs of any defect,no. 1216 stamped on float bowl so what washers should be fitted,tried,fabric washers with aluminium washer sandwiched between,no luck,rubber washers wont slip down length of bolt far enough,possibly incorrect securing bolt,getting complicated.

[bmcecosse]

Does this diagram help? Is your leak from the jet assembly - or from the float bowl mounting?
http://www.sucarb.co.uk/TechnicalDetail.aspx?id=91

[MarkyB]

Does petrol drip out all the time or just when the ignition is on?
Also do you have a standard SU pump fitted?

[bootlid]

I have now a proper diagram which shows two differant securing bolts which hold up the float chamber,the one in my set up has two fibre washers with an aluminium washer in between,between the bowl and carb body another fibre washer is fitted,this is where the petrol is leaking out,the diagram also shows a shouldered bolt with two rubber grommits and a dished aluminium washer,which one is correct for my carb i dont know,