Amal 289?

[richard norris]

I am trying to sort out the carburation on a 3 speeder which has a 1 3/16″ choke premonobloc Amal. Is this a 289? And has anyone got the throttle valve diameter to hand? The walls are thin and I wonder if it has been bored out as the current valve looks a bit home made. Advice please…

[BRIAN MARSHALL]

Hi Richard, Is there anything stamped on the edge of the mounting flange ? A genuine 289 has a much bigger mixing chamber than a 206/151R. Many components are interchangeable, including the entire float chamber assembly, throttle stop screw, primary air screw, jets, cable adjusters,etc.. BUT, some other items, whilst apparently interchangeable will give you endless problems ! A major culprit is the bottom nut that retains the float chamber banjo to the mixing chamber. Also the hexagonal tube that the main jet screws into is a different length. SO…. You must firstly make sure that you don’t have a mongrel carburettor made up of some wrong items, or you never will get it sorted ! An original 289, as fitted to the 1939 Clubman Special, is 1-3/32″ choke diameter, not 1-3/16″.
Regards,
Brian

[richard norris]

Thanks Brian, this is the 1931 Sprint Special from Argentina (apparently) bought by my brother at Bonhams this April. It has a side mounted carb like a 2 speeder and the carb body is devoid of markings. The bike starts remarkably easily but runs rich even with the needle well down. Before weakening the throttle valve I have I want to male sure that the rest is ok and to know what I have.

[BRIAN MARSHALL]

Hi Richard, If it is brass bodied and clip fitting, it will probably be the type fitted to early post-war Vincents, so you can easily get spares for them. 1-3/16″ is really too big for anything but racing, and an unmodified one will be a better proposition.
Brian

[richard norris]

That’s very useful Brian, thanks. As it happens the body is aluminium so all very interesting. Float height is in the right area. I quite agree about the large bore, I’m surprised that it runs so well at low speed, prob the rich mixture. It doesn’t spit – yet. I’ll probably fiddle with the slide in the knowledge I can ditch the whole thing and start again if necessary. If you have a 289 slide I would love to know the dia.

[dave bushell]

Amal carb 289 is the the same size as the type 29 (with the 3 point fixing as used on the Scott Clubman) and has a bore of 1-1/8″ not
1-3/32″. I have one fitted to my prototype Clubman Special.
Dave

[richard norris]

You are right Dave, it is 1 1/8th

[BRIAN MARSHALL]

Hello Richard, Dave, and anybody else who is interested, I have consulted the Amal listing for the 1939 Clubman Special, and it is listed as the 29-005, size 1-3/32″ (!!), jet 200, slide 29/3, needle position 3, float chamber 92. As I previously mentioned, the entire float chamber is exactly the same as the type fitted to the smaller Type 6 carburettor, but that will be of no use to Richard with his side-mounted, clip fitting type. I have carefully measured the diameter of a slide on an unworn area still carrying the satin-chrome (?) original finish, and it measures 1.3065″.
I can only surmise that with Dave’s bike being a prototype, it perhaps has a carb that is of a different choke size to that decided on for production models, and obviously Richard’s carb is not from a Clubman Special, is not a 29-005, and so could be of any size !
Brian

[dave bushell]

Amal pre monobloc carburetters initially had brass bodies and separate float chambers, and were available in 4 body sizes each of which were available in several bore sizes; these were known as types 4, 5, 6 and 29. They were fitted from 1929 until 1933 when the body material was changed to zinc die cast alloy and the model numbers were modified to types 74, 75, 76, and 89. They can be distinguished from the later types because these have four air holes around the base of the body which the next type does not. In 1939 types 274, 275, 276 and 289 were introduced; these have two internal primary air passages in the base of the jet block. A later version with an ‘R’ suffix denotes that the primary air passage hole was moved to the air intake.
Each type number mentioned above indicates a different size of casting. Each casting was to any one of several bore sizes.
I have only found one reference to a type 29/89/289 carb with a slide bore of 1-3/32″. All other mentions in various tech and motorcycle publications refer to 1-1/8″ diameter slides, and I think that this was the size fitted to the Clubman Special.
Dave

[BRIAN MARSHALL]

Hi, I trust that Dave means choke diameter in his last sentence, not slide diameter, as of course slides are wider than the choke diameter, or air would leak by the sides of the slide. I have now had chance to measure three Type 29 carb choke sizes. All are brass bodied and have the primary air inlet in the choke tube rather than externally around the bottom of the mixing chamber. One carb is a genuine 29/005 Clubman carb., and it is 1-3/32″ size. Then a clip-fitting version, stamped 289/032R, is also 1-3/32″. Finally I have what was another clip-fitting Type 29 that has had a Scott three-hole flange grafted onto it, and the number stamping is no longer legible. It has a choke diameter of 1-1/4″ !!
Brass bodies continued to be made after 1933 for some bike manufacturers, including of course Scott, as even Brum Scotts have brass carbs, but they were very possibly old stock. Early post-war Vincents were also fitted with brass carbs..
The change from external primary air holes, to an internal one adjacent to the bellmouth thread, was at the behest of Government buyers, who very sensibly insisted that all the air entering the carburettor could be filtered, including the primary air.
Brian

[richard norris]

Hello again and Happy New Year everyone, thanks for your helpful comments.
I now find in faint lettering “229F/1D” on the inlet side. The carb has been bored out and a home made slide looks good. It is appreciably deeper than a standard 276 slide though and this accounts for the richness of the mixture I think as the needle is held higher up. Also the needle looks home made or adapted from another.
Choke size is 1.10″ and it fits a stub of 1.27″ o.d.
Any thoughts?

[BRIAN MARSHALL]

The problem with all modified items, no matter how well the work has been done, is that you don’t really know what you have got, unless the modifier tells you what he has done and why he has done it. All the parts have to be compared to standard items and carefully measured. It also muddies the water and confuses future owners.
Brian

[richard norris]

You are dead right Brian. Luckily the pilot and cutaway seem pretty good and I am hopeful but of course it should be properly sorted by an expert. I intend to get that organised once I have maxed sure the motor is a otherwise ok.

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