Fuel leak from carb

[Ian Wegg]

I've been having the same problem. I took the float valve out today and checked it was working properly (by blowing through it and pressing the pin to make sure the valve closed). All appeared ok but there were no washers that I could see.

I took this video which demonstrates the issue:

https://www.youtube.com/watch?v=OmvNr6zsyu4

I'm guessing that the correct washers may well fix the problem. I see that Burlen sell the needle valve for £12 so I'm thinking of replacing it anyway. They also sell a rebuild kit ("ZRK48"), can anyone tell me what that contains? Any other thoughts would be most welcome.

[John Mason]

I sorted my carb leaking and slight poor running problems by lowering the level in the float chamber by fitting an annealed copper washer under the needle valve. I just looked into my assortment of copper washers and found one about 1/8” thick.

John Mason

[Bob Culver]

Few cars have the original pump. And some have the wrong lever. Pump springs vary in strength. The packing of the pump from crankcase also determines pressure. Not easy to check but simple gadgets were common. (Note hand operating does not duplicate running situation)

[Graham Barker]

I watched the video of the carburetor leakage and it looked like a worse version of a leakage problem that I had with the same type on my 1937 Ruby. I found that the leakage was coming out of the banjo fuel pipe union. I didn't want to screw the banjo fuel pipe union any tighter because it is easy to strip the thread in the soft metal of the carburetor. So eventually I found a sealant that was resistant to petrol and applied that to the disassembled banjo union faces and reinstalled it.  Problem solved.

[Ian Wegg]

Thanks, Graham, you are right.

I thought the fuel was coming out of the little hole on the top of the carburettor, but on looking again I can see it is flowing through that hole from the pool on the other side. As a test, I wrapped rags around the union and they quickly got soaked while the top of the carb remained dry.

I disassembled the union and got a very sticky bitumen like substance around my fingertips, which took ages to remove and took my fingerprints with it! I think the previous owner had had a go at sealing the joijnt. The bolt head is in a bad way so I have ordered a new union bolt from A7 Components plus a set of new fibre washers. I'll cross what's left of my fingers and hope that fixes it.

To tie up a loose end and answer my earlier question -  Burlen's Zenith rebuild set does include the needle valve.

Thanks for the help.

[Graham Barker]

Hi Ian, 
I am surprised that others didn't also suggest leakage at the banjo. I have seen leakage there on other local Austin Sevens. 
Go carefully with tightening the banjo bolt. I wrecked one carburetor top by stripping the thread when tightening the bolt. New fibre washers and dressing the faces still didn't cure the leak. Hence the need for sealant. 
Cheers 
Graham

[Ian Wegg]

Go carefully with tightening the banjo bolt. I wrecked one carburetor top by stripping the thread when tightening the bolt. New fibre washers and dressing the faces still didn't cure the leak. Hence the need for sealant. 

So out of interest, how did you fix the stripped thread? Did you get a new top or did you replace the whole carb? Any suggestions for a supplier gratefully received. Also what sealant did you use?

The new bolt arrived and although I tightened it carefully I think the thread must have already been stripped as it just turns. No amount of Hylomar can stop the spray of fuel.

[Graham Barker]

Hi Ian, I obtained a second hand carb from another Austin 7 owner.  I am away from home for another day. When I get home I will look up the name of the sealant. 
Cheers 
Graham

[Bob Culver]

Helicoils are expensive and involved. The purists wince but later Zeniths had 1/2 " UNF and anyone involved with 1950s cars will likely have some. The stripped 7/16 can usually be tapped to take. Taps cheaply available. I have recovered several this way but being associated with the Jowett Club have a vast supply of 1/2 inch unions.
Red fibre can be purchased in sheet form and washers made.l. In this age of O rings often an o ring inside a spacer ring or washer will solve a problem and need not be very tight. Awkward without a lathe although much can be done with a drill.

[Graham Barker]

The sealant that I used is JB Weld Water Pump and Thermostat Housing. It is RTV Silicon. The fine print led me to believe that it was resistant to petrol. It is still holding well after 8 months.