Leaky Amal 274 pre monoblock carb..

[casperboat]

Hi again.. I just can't stop this carb from leaking. The float is now doing its job, but the leak is from the thread in the main body of the carb.
I've attached pictures as it's easier to see where it's leaking than me trying to explain it. I've fitted a new fibre washer, I tried an O ring, I tried making a gasket from gasket paper, but it still leaks. I did wonder whether that slot in the thread could leak, but with the carb together I can't see it to check..
I've run out of ideas..
Gary

[iansoady]

There should be a washer on the mating faces there. 25 on the diagram. Can't remember whether it's paper or fibre.

It looks as though it comes with the set (no.50). Whatever you do don't try to seal it with silicone......

Pic is from Hitchcock's who I usually use.

It could be that the float level is set too high as well.

[cardan]

Hi Gary,

I think you'll find that the only way for fuel to get above the jet block (and then leak out) is via the jet.

The fuel level is probably just above the top of the jet, rather than just below where it should be. Try lowering the fuel level a mm or so.

Leon

[casperboat]

I've fitted a new washer, but that hasn't stopped it. If the float level is too high, will that allow fuel to leak out from that slot in the thread i can see?
Gary

[casperboat]

Hi Gary,

I think you'll find that the only way for fuel to get above the jet block (and then leak out) is via the jet.

The fuel level is probably just above the top of the jet, rather than just below where it should be. Try lowering the fuel level a mm or so.

Leon

Ok, sounds like a plan. For a newby to carbs, how will I go about lowering the float fuel level.

[mini-me]

It would help if you put up more pics of the float chamber attached to the carb, For the moment forget faffing with petrol levels.

#1the large union gasket is best made from thick graphited paper.
#2 the union nut comes in several sizes, a longer one will lower the flat chamber itself  and vice versa.
#3 the float chambers come in many angles; the top should always be horizontal, not even a  teeny bit wonkey.
#4 take off the float chamber and dismantle it; turn it upside down, insert float needle and GENTLY tap it into its seating. I suspect the needle is not properly sealing. If it was not sealing at all it will piss out the top of the float chamber anyway. It should have no ridges onthe conical part, somtimes a gentle lapping in with brasso will improve matters.

This is mostly the result of modern "restorers" asembling carbs from autojumble boxes; On top of that I find that there is nearly always a bit of a weep from these carbs anyway; They are after all a 80 yearold design.
There is no float level 'adjustment' as is understood  in the way with modern carbs.
A O ring is useless.

You could of course have some defect like a hairline split or other distortion somewhere.

[casperboat]

I've attached some pics of the carb. You can see the O ring under the float chamber top, I was told that may help stop it flooding out the top, which it has. You can also see the new red fibre washer in the nut, it was only cheap, about 20p, but I had assumed they were all the same..
I was thinking, when I tickle the carb and it floods out the top hole, before starting, will that mean that until I start the engine, fuel will always leak out of the jet hole in the thread of the main body of the carb, making it appear that it's the thread that's leaking? The last time the carb was leaking, it stopped leaking once I started the engine..
When I remove the top cap from the float chamber, with the fuel tap on, the fuel stays level.
I am more into old diesels than petrols so I have little experience of carbs, and I may end up having to take this to someone who knows what they are doing.

If it means anything; nothing leaks out when I turn the fuel tap on, until I tickle the float..

Would it be worth fitting 2 washers about the banjo, to lower the float chamber?

[iansoady]

I was thinking, when I tickle the carb and it floods out the top hole, before starting, will that mean that until I start the engine, fuel will always leak out of the jet hole in the thread of the main body of the carb, making it appear that it's the thread that's leaking?

Yes of course. I hadn't realised that was what you meant.

FWIW you should never be tickling it so fuel comes out of the top - that's far too much. A few seconds once the needle has closed should be enough. The way it is, all you need is a backfire (or indeed some petrol spilling on the mag) and you may well end up with a conflagration.

It sounds as though you don't actually have a problem (other than user error.......)

[casperboat]

I'm not surprised by "user error", i'm learning as I go along, but that is why these forums are so useful. Sounds like I should just go out in this fine weather for a ride and see how it goes.
Thanks.
Gary

[iansoady]

That's it!

make sure you have a charged mobile & breakdown number.......

[mini-me]

the o ring under the float chamber top is pointless as the fuel never reaches that level.

Do not faff about with extra washers for the union, likely you'll strip the thread as  there is not a lot of it, original washers are quite thin less than a 1/16th; if your is thicker you could always soak t in hot water to soften it.
Do not block any of the holes in the base of the jet block.

These carbs are ,as I said, always a bit leaky and messy especially if you overdo the tickling; which is why you never see a vintage motrcyclist picking his nose with his index finger

It does sound as if you are having a problem with your user habits though.

[casperboat]

the o ring under the float chamber top is pointless as the fuel never reaches that level.

It does sound as if you are having a problem with your user habits though.

Someone recommended I put the O ring in, not to form any seal, but to raise the top in case it was somehow preventing the float from rising enough to stop the fuel, because a while back fuel was pouring out the top of the float chamber.

I have been and started it again and it ran fine with no leaks, I did as suggested and only held the float tickle thing down a couple seconds.

[mini-me]

Someone recommended I put the O ring in, not to form any seal, but to raise the top in case it was somehow preventing the float from rising enough to stop the fuel,

A little bit of knowledge etc etc etc

anyway it seems you have sorted it now.