Leaking carburettors

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Can anyone help?
I have a 1963 650SS with the original paired 376 Amal monobloc carbs with the right chopped one connected by a banjo on the extended main jet holders to the left float chamber. Both carbs are leaking fuel from the lower fibre washers on the banjos. It is a significant drip that will empty the float chamber in 10-15 minutes, not just a bit of weeping. I have tightened the nuts as much as I dare, have used new fibre washers that I soaked in fuel for 24 hours and tried some Blue Hylomar as well as the washers to no avail. I took the banjos and jet holders to Burlens and they felt they were in good condition. What can I do to stop this leak short of replacing the whole banjo and main jet holders assembly with new components? Am I doing something stupid ?

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Carb1.jpg

Carb2.jpg

Are you certain that the…

Are you certain that the leak is from the lower fibre washer? It may just be collecting there from a difficult to spot leak from above.

A couple of things to check:

Is the sealing surface on the carb body good?

Are the threads bottoming out, resulting in not enough compression on the banjo sealing washers?

WHY?

Why are you soaking the washers in Petrol?

Are the banjos square to the…

Are the banjos square to the body?

Check without the fibre washers

Thanks for all your…

Thanks for all your suggestions.
The leak definitely seems to be coming from the lower of the fibre washers. It is dry at the junction of the upper washer and carb body. I know that the main jet cover nut can weep a bit but this doesn't seem to be happening here. The face on the carb body is clean and flat. I soaked the washers in fuel because someone suggested that this makes them swell a bit and create a better seal. Didn't work in my case. Without washers the jet holder doesn't screw into the carb completely but seems to with washers in place . I could try with two washers between carb and jet holder. The banjos appear square.
I have removed the carbs from the bike to get a better look. Even with the jet block locating screw in place I can move the jet block up and down in the carb body. It's a long time since I dismantled a monobloc and I can't remember whether the screw is supposed to anchor the block completely or just stop rotational movement. Is it the screwing in of the main jet holder that fixes the block in position. The carbs are old and haven't been used for 35 years but they did not leak when the bike was last running so it seems like something that I have done in the re-assembly is the problem.

In my new monoblocs, the jet…

In my new monoblocs, the jet block moves when the bottom nuts are slack. The side screw just holds position. I'm not going out to undo mine but I wonder if the banjo is simply too thin? Is it standard? I had a persistent leak from a banjo on a TT carb. Measured it all carefully, checked flatness and smoothness. Finally cured with a little Wellseal. Still don't know what was wrong.

Leave the washer out, fit…

Leave the washer out, fit the banjo fully and measure the gap with feeler gauges.
Measure the thickness of your washer with a vernier gauge. It should of course be more than the gap measurement.

Do the checks…

....as suggested above. If they don't show you a physical problem, clean down and dry everything. Then puff talc with a rubber bulb or similar over the lower end of the carbs and fuel pipes. Fuel on and without tickling leave the level find itself, then switch off. Watch where the first wet track emirates from.

I'd be suspicious of jubilee clips on plastic pipe work. Personally I'd throw both and fit rubber with appropriate crimps. The action of a J/clip on thin wall plastic and small diameter could distort the shape of the pipe.

Jon I put the jubilee clips…

Jon

I put the jubilee clips on to see if they would stop the leak but I note your comment re rubber tubing. The leak does seem to be coming from the lower washer but good idea re talc. I am double checking all the faces for flatness and checking the threads in the jet block.

Michael

Excellent suggestion. I will measure tomorrow.

David

The banjos are the original fittings. At least they were on the bike when I bought it in 1971!

I and several of my club…

I and several of my club members have found that the new fibre washers suppled by carb specialits do not now do the job . Even very tight still leak . One member has made up annealed copper washers that solved the issue.Old well used orriginal fibre washers still work !!

Dowty Washers

My brand new and very expensive replica Amal 76 carb leaked terribly from first use. I purchased a box of Dowty washers as replacements for the near useless fibre washers. Positive result.

Norton Owners Club