A7 Amal concentric premier carb

[iandontomjim12]

Hi All, Thanks in advance for any help you can give.
I'm new to BSA's and old British bikes in general.
I've just purchased a 1953 A7 plunger. I've managed to get the bike running quite well but no amount of tinkering will stop fuel leaking from the pre-monoblock Amal.
The float needle does seal off but petrol still leaks from the the tell tale in the bottom of the main carb body, above the union nut when the bike is not running. The carb has had new fibre washes but shows signs of previous abuse and I don't believe the correct float bowl is fitted.
 I'm thinking of changing to a new Amal premier concentric carb but could do with some advice on compatibility and what size to fit. 

[Rex]

Go to Hitchcocks and tell them the bike it's for and they'll do the rest.
I did for my plunger A7 (and other bikes) and I'm very happy with Premiers.
Only issue (although it didn't matter to me as such) was that the carb mouth ends up close to the frame tube so I fitted a bell-mouth. There isn't much room if you want to use a proper air filter.

[Swarfcut]

     The 276 Type carb originally fitted has a remote float chamber, this can be lowered  by additional fibre washers between the float bowl banjo and the mixing chamber body union nut. This will lower the fuel level in relation to the needle jet outlet and is worth a try. From description the fuel level is simply just a bit too high. A missing  or too thin sealing washer under the jet block can also raise the level by raising the union nut and float bowl so that fuel overflows the needle jet.

    Later  Monobloc was a popular conversion back in the day, but as noted, on Plunger bikes it is a tight fit and no room for a filter connection.  If you still have the rare and relatively expensive original air box, well worth persevering with the original carb type. Set up properly they work well.

 Swarfy.

[muskrat]

G'day Ian 
I agree with Swarfy about keeping the 276.
BUT I'm buggered if I could get mine to work well 30 odd years ago on my A7 plunger so went concentric. I just recently up graded to a Premium and am very happy with it. No room for an air filter.
Unfortunately my settings won't suit you as mine has alloy SS head, 357 cam, big valves and straight through exhaust  . Rex may have jet sizes.
Cheers

[Greybeard]

     The 276 Type carb originally fitted has a remote float chamber, this can be lowered  by additional fibre washers between the float bowl banjo and the mixing chamber body union nut. This will lower the fuel level in relation to the needle jet outlet and is worth a try. From description the fuel level is simply just a bit too high. A missing  or too thin sealing washer under the jet block can also raise the level by raising the union nut and float bowl so that fuel overflows the needle jet.

    Later  Monobloc was a popular conversion back in the day, but as noted, on Plunger bikes it is a tight fit and no room for a filter connection.  If you still have the rare and relatively expensive original air box, well worth persevering with the original carb type. Set up properly they work well.

 Swarfy.

My '55 had it's original 276 carb. I put a new slide and needle and needle jet in it and used the original filter box with a modern, (modified) filter. I had no problems starting or running with that setup👌

[Swarfcut]

 Just a further note about the original 276 Carb.  The float needle on the bottom fed  float chamber can be found with two locating grooves for the float clip. We always assume this is in the right groove if you have two, so something else to check. Clip on lower groove will raise the needle in relation to the float, and so lower the effective fuel level in the float chamber and  this could be the root cause of the original leak. Also with the inlet tract cast into the head at a slight angle, the float chamber needs to be the  correct one for the bike to maintain it in a near vertical position, and rotated in relation to the carb body to best achieve this.

 There are a good few variants of float chamber listed.

    https://amalcarb.co.uk/pre-monobloc/76-276-series/float-bowls.html

 Use to identify what is required, usually plenty available at the jumbles/swap meets I go to. Hard to justify these new prices though.

 Swarfy.

[iandontomjim12]

     The 276 Type carb originally fitted has a remote float chamber, this can be lowered  by additional fibre washers between the float bowl banjo and the mixing chamber body union nut. This will lower the fuel level in relation to the needle jet outlet and is worth a try. From description the fuel level is simply just a bit too high. A missing  or too thin sealing washer under the jet block can also raise the level by raising the union nut and float bowl so that fuel overflows the needle jet.

    Later  Monobloc was a popular conversion back in the day, but as noted, on Plunger bikes it is a tight fit and no room for a filter connection.  If you still have the rare and relatively expensive original air box, well worth persevering with the original carb type. Set up properly they work well.

 Swarfy.

Thanks for the advice. I've added an extra washer as you suggested and it's worked a treat. Much appreciated.
As i do have the original air box I'll do what i can to retain the original carb.

[Swarfcut]

 Good to know some success for once. The airbox with the outlet on the side is the same for A7 and A10 Plunger bikes and uses a rubber moulded right angle connection to the carb. Because if the differing block heights and carb sizes the connectors are just that bit different and don't interchange. At one time the A7 type was a common repro part, which I thought strange on my understanding that the A10 was a more popular option. Dunno if this availability still applies but the A10  repro version was scarce in comparison. NOS items don't age well.

 Swarfy

[Rex]

Just a further note about the original 276 Carb.  The float needle on the bottom fed  float chamber can be found with two locating grooves for the float clip.

if you look very closely you can see "P" and "C" on the grooves, one indicating the position for a plastic float and the other a copper float.

[Greybeard]

Good to know some success for once. The airbox with the outlet on the side is the same for A7 and A10 Plunger bikes and uses a rubber moulded right angle connection to the carb. Because if the differing block heights and carb sizes the connectors are just that bit different and don't interchange. At one time the A7 type was a common repro part, which I thought strange on my understanding that the A10 was a more popular option. Dunno if this availability still applies but the A10  repro version was scarce in comparison. NOS items don't age well.

 Swarfy

I bought a newly made connector from someone in America. It was made of something pretty firm, deffo not rubber. It worked fine though.