Hi, Your problem could be with your petrol pump. If your pump fails to go into idle mode when the carb float chamber is full the extra pressure allows petrol to get by the button valve in the top of the carb.The pump is designed to stop pumping once the float chamber is full. I believe this is done by letting the operating Cam idle until more fuel is required.

John Mason

Location: Nottinghamshire

John Kenneth, you might think that the needle valve is shutting off effectively, and indeed it may be doing so under engine not running conditions but, I would put money on the needle valve (possibly due to vibration) not remaining shut when the petrol in the float chamber has reached it's operating level with the engine running. The only way the carb. can drip is if the fuel level in the float chamber becomes too high. The problem can't really be anything but the needle valve leaking (maybe as a consequence of fuel getting into a punctured float).
If the needle valve closes effectively the back pressure holds the pump diaphagm down causing the pump actuating lever to ride on it's cam but not to be operating the diaphragm i.e. not to be actually pumping.

Ian Mc.

Location: Shropshire

Hi John

Many thanks for you help,I realize that the pump should idle when the float valve shuts I have considered a new valve,I ground the needle in as best as I could (being a sealed unit).I ran the engine again after my appeal on the forum and again no leaks until the engine had been running for about 5 minutes then petrol was spotted flooding on on the carb casing above the float chamber.There are 2 holes there and it appears the petrol was coming from there.
I will take note of your suggestion

Many Thanks

John.

Location: Malton North Yorks

Hi Ian

Many thanks for your help on my dripping carb.I do agree that if the valve is working petol should not get through.I have merely blown through the vave so I will get a new valve.

Kind Regards

John

Location: Malton North Yorks

Good idea John

Ian Mc.

Location: Shropshire

It is standard workshop manual info but may not be universally known. I dunno the recommended pressure for a Seven but for other Zeniths 1.5 to 2.5 psi is typical. The spacing of the fuel pump from the crankcase alters pressure. Sevens have acquired pumps from many sources. More than one internal spring is available, affecting pressure. (Curiously a very low pressure is specified for some SUs, such as 1950s Minor).
It is claimed old hard diaphragms can raise pressure. The pressure from any priming lever is not the running pressure.

For those with lots of tubing and patience 1.8 psi is a column, 5 ft 6. A bit more than from a low scuttle tank!

Location: Auckland, NZ

Thank You Bob

That is another possibility to check out.That should eliminate the pump.
I did not mention that I noted petrol was coming out off the top ,above the float chamber.There are 2 holes about 16th inch dia.I have not looked yet on the 26VA diagram.

Cheers

John

Location: Malton North Yorks

Iv had the same problem with mine for a while now, it only drips after a run & only drips for a couple of minutes. As a temporary measure & to save any potential flames, Iv fitted (with the use of magnets) a small baking loaf tin beneath the carb on the plate above the exhaust. Once the dripping has stopped, I pull it off of the magnets & pour the content back into the tank 😉

Location: North Wales

Hi
Well I got a new needle valve and Ian was right,no dripping at all when engine is running and just a few drops when I kill the engine.Many thanks.

Yeah I did that a couple of months ago, didn't make a bit of difference on mine.
A bigger problem I have is failing rubber seals on my recently purchased replacement fuel pump, it appears that the Chinese don't realise that you need neoprene rubber for a fuel pump

Location: North Wales