which carb?

Sorry can't help with numbers but I'd start off by lifting the needle to help sort out the 'odd backfire'.

You can find all the carburettor data you need here:

http://archives.jampot.dk/technical/carburation/amal_monobloc__numbers_type_and_use.pdf

As you say, the 389 / 17 was supplied for a Francis Barnet 250. Being a 2-stroke, the spray tube is probably cut away at the rear (I have one of the same id number), in the same manner as a Concentric supplied for the Commando. I haven't tried this, but I have a suspicion that this development may be good for many large-choke carburettors on big cylinders.

I believe that the cutaway spray tube for 2 strokes only appeared on Concentrics not Monoblocs. But I could well be wrong.....

John - have you found a filter that might fit? I'd like to have the option of fitting one to my prewar bike. Ugly I know, but I'd like to preserve my engine.

Also: my (late) friend had a Featherbed ES2, and there was a hole in the plate between the oil tank and battery box for a filter to fit between the two. But it was dead centre, and the carb is off centre - so the hole would only match the twin engines with single carb. But then I think he said there was an ES2 filer in the parts list... have you found one, or is this a known problem and were they never a factory fitment?

Well, I have a 389 / 17 which came to me with a cut-away spray tube, and it looks like a factory job not a back-yard modification. For now, I have fitted a jet block with a normal round spray tube from a damaged 1 1/8" carb body.

I have a Spanish-made Monobloc of 30mm bore, and must take a look at it to see if it has the same cut-away spray tube

Paul

Previously ian_soady wrote:

I believe that the cutaway spray tube for 2 strokes only appeared on Concentrics not Monoblocs. But I could well be wrong.....

Anteriormente john_day escribiÃ?:

Anteriormente, David Cooper escribiÃ?:

John, ?has encontrado un filtro que pueda encajar? Me gustarÃa tener la opciÃ?n de colocar una en mi bicicleta de antes de la guerra. Feo lo sÃ?, pero me gustarÃa preservar mi motor.

TambiÃ?n: mi (tarde) amigo tenÃa un Featherbed ES2, y habÃa un agujero en la placa entre el tanque de aceite y la caja de la baterÃa para que un filtro se ajustara entre los dos. Pero estaba en el punto muerto, y el carburador estÃ? descentrado, por lo que el agujero solo harÃa coincidir los motores gemelos con un solo carburador. Pero luego creo que dijo que habÃa un archivador ES2 en la lista de piezas ... ?ha encontrado uno o es un problema conocido y nunca fue un accesorio de fÃ?brica?

He instalado una pernerita de hitchcocks con gasa ... parte no am3891066b

pero tambiÃ?n he puesto un poco de gasa de acero inoxidable en el exterior. He enviado un filtro chino con un desfase de 45 grados y te avisarÃ? si encaja cuando llega

Estimados amigos:

Ha colocado un filtro que entra muy justo en mi Amal, pero tambiÃ?n en el caso de que no haya polvo entre (polvorientas zonas) y el motor estÃ? nuevo.

EnvÃo archivo adjunto

I have just found the 389 / 30 I bought in a misguided moment a number of years ago. I was told that it was off a Spanish two stroke, the tech page posted by 'Jampot Archive says that the / 30 stamping indicates Greeves 197cc.

What I find interesting is the spray tube, which has an angled cut-away at the rear as done to the spray tubes for Concentric Mk 1 on Triumph Tridents. I also have a 389 / 27 (Francis Barnet 249) which has its choke tube rear part completely cut away like a Mk 1 for a Commando.

Another oddity on this 389 / 30 is that the jet holder appears not to have a main jet, there's just a large nipple at the bottom where a main jet cover nut should be. The actual main jet sticks out from the right side of the float chamber at the bottom, and looks like an oversized pilot jet. Its output feeds into the jet holder. I have never seen anything like that before. Is this a known type of Monobloc? Are these main jets obtainable?

Paul

Previously ian_soady wrote:

I believe that the cutaway spray tube for 2 strokes only appeared on Concentrics not Monoblocs. But I could well be wrong.....

That sounds interesting Paul - do you have a picture?

I took a couple of pictures and tried to attach them, but they were too big. I will email them to you, and you can post them for me if you like.....

As I said, the main jet is like an oversized pilot jet. I suppose it is slightly easier to get at the main jet, and its sideways, which may be good if there are access issues.

Amal would have had to make an entire new die to cast this body, so they went to a lot of trouble to create this carburettor.

Since I posted last about this carb, I have come to the conclusion that the 30 stamping on the right side of the mounting flange says 30mm bore, not 389 / 30, being a Greeves 249 carb. My vernier says that it's really 29.6mm on average. I have no idea what Spanish two stroke it was made for.

Previously ian_soady wrote:

That sounds interesting Paul - do you have a picture?

I took a couple of pictures and tried to attach them, but they were too big. I will email them to you, and you can post them for me if you like.....

Previously ian_soady wrote:

That sounds interesting Paul - do you have a picture?

Will do - ian at iansoady dot org dot uk.

Carb photos attached. I must say I've never seen anything like them......

For some reason the second one downloads rather than being viewable and I don't seem to have the privileges to delete it......