Leaky carbs...

[matt78]

Hello.

Concern regarding my 100/4 carbs : I recently bought the car, with the information that the carbs had been completely overhauled - some of the gaskets I can see actually seem to be new. The car starts and runs very nicely.

During several electrical checks of the wiring, I had to switch the contact ON, causing the fuel pump to run (engine not running). I then noticed that some fuel leaks appeared at the bottom of the jets (still not sure of the exact location of the leaks' source).
Incidentally, the choke was "on", so my questions are :
- is this normal ? I guess it is not, but as the choke was engaged, maybe it could have worsen the situation ?
- if this needs to be corrected as I think it should, do you think that it would be useful to - again - overhaul the carbs by using the full SU kit, or is there any chance that the leaks might be caused by worn-out "mechanical" parts (jet, bores...) ?

Thank you in advance for your replies (silly question maybe, but I don't know these cars, and don't want to replace parts that don't deserve it).

Regards,

Matt

 

[blueskies]

Those likely are H4 carburetors. If so, they have two seals located in the lower part of the carb that go around the jet - one above and one below the small spring that fits around the jet. There also is a larger rubber seal - O ring type - directly above the big nut just above the jet adjustment nut. You might begin by tightening that big nut, taking care not to turn the smaller nut below it that adjusts the jets. If that does not fix the leak, it might need the smaller seals mentioned above.

My acquaintance with H4 carbs is recent and I do not claim to be an expert on them. I also need a rebuild kit for my H4 carbs.

 

[BigGreen]

To find out the type of carburettor, see the SU website https://sucarb.co.uk/

Lots of pictures and instructions

Succes

 

[bob hughes]

Just throwing this into the mix - the floats are there to prevent fuel from entering into the jets unless there is a draw on the fuel through the carbs - i.e. the engine turning over. Could it be that the floats need adjustment ?



Bob

 

[EV2239]

The floats and their needle jets are set so fuel is in the jet and a little below the bridge in the main throttle body.

This means that the jet housing below has fuel in it which may leak. The jet is lowered a 1/4" when the choke is pulled and it slides up and down in compressed cork gaskets that are rarely completely leak free. Therefore the lower part of the carburettor may well be wet, but not dripping. Experience alone tells you when it's time to change the cork seals.

The Burlen Fuels/SU website will have exploded diagrams to assist in understanding the vagaries of these carburettors.

 

[matt78]

Thank you for all your replies and this useful link. I think I'm in for a new overhaul :grumpy:

Matt