Misc: Carburettors Amal Carburettors Dripping Badly

[Magnetoman]

I added fuel to this figure to show where the correct fuel level needs to be.

The fuel level needs to be near the bottom of the pilot air hole, but the figure clearly shows why if it is any higher it will leak out that hole. If yours doesn't ordinarily leak, but continues to after you tickle it, it could be more that the float needle is hanging up in the holes it rides in at the top and bottom rather than not sealing at the seat.

Another common source of continuous seepage is the joint where the big "nut" attaches to the main body. If the sealing washer in there doesn't completely seal, which is often the case, fuel works its way up the threads and out onto your foot.

 

[greg brillus]

The side bowl carbs can and will always leak........mostly if the fuel level is too high, but then this in 90% of cases is due to leaking fuel taps. They should not leak so much if the bike is dead upright, but on a side stand the opposite side carb will tend to drip.

 

[oexing]

The big fibre washer seal is pretty hard for coping with less than perfect components on an Amal. An easy mod is to reduce the o.d. of the washer for a thin o-ring. The washer is 1.1mm thick so a 1.5mm o-ring is great for easier sealing. You don´t want to heave on the big nut for getting the joint fuel-tight when the carb is half a century old. So the fibre sets the float position and the oring seals the lot.
Another overlooked leak is above the big nut in the slot for the orientation pin. On some jet blocks there are two useless drillings , one is open to air and can leak while parking. The fuel level is higher than the position of the drillings so there. The hole could be pluged with solder or a bit of o-ring or so.
But even then, fuel can leak down along the jetblock from pilot system drillings and creep up the big thread and wet the carb at least. So a smear of Hylomar on the flange of the jetblock will seal it to the carb body, the o-ring around the fibre washer seals from below - hopefully.
The float needle taper can be restored by twisting it between fingers with fine abrasive paper when a ridge has formed. So then a very fine grinding paste will lap the lot in the valve seat for a good sealing.

Vic

 

[Texas John]

I would not try unscrewing the nut under the jet block if the carb is still bolted to the manifold. << SNIP >>The Mazak faces where the fire washer fit on the float chamber arm are very often corroded and need careful dressing with a fine file. << SNIP >>
Brian

Brian, What is a "fire washer"? How does one remove the jet block (without breaking anything)? Thank you.

 

[greg brillus]

The lower carb base nut normally has a gasket material type washer that is reasonably soft, well most all the ones I've seen/used on these side bowl carby's.........Heat will usually allow the brass jet block to be removed without too much difficulty. Just for interest sake, the lower carb body cap nut is available in many different heights, at least 4 for the type 76 carb's and possibly similar on the 29's this makes for many variations in the bowl heights.

 

[chankly bore]

I think the two answers are "fibre washer"-English spelling plus typo. and warmth- boiling water and using the needle jet thread and a small slide hammer device. The thread is 1/4" B.S.F.

 

[Texas John]

Thanks Charles - It had not occurred to me that fire was a typo for fibre.
I have a 276 on an Ariel that I had tried to disassemble some time ago and finally gave up.
Lucky I did not damage it as I later read they are fairly fragile.

 

[Gerry Clarke]

The original carbs. do not leak if correctly set with the correct thickness washers and vertical orientation on the stubs. Does anyone really think that fuel seepage from carbs. or dodgy fuel taps would have been tolerated by cash strapped enthusiasts in Britain after the war when fuel was rationed? Fuel rationing only ceased in mid 1950.

Gerry

 

[Mike 40M]

A workmate works well for adjusting front wheel bearings.

 

[danno]

They should not leak so much if the bike is dead upright, but on a side stand the opposite side carb will tend to drip.

Yes. There's no dripping when the bike is upright. When leaned over on the left sidestand, the right carb starts leaking onto the rear fork frame.
I'll follow some of the tips given to try and stop it.