20T Correct carb & settings.

[Spike1947]

Hi chaps,

I have a 1957 20T with a 9E engine but it has a 250cc barrel conversion.

It has an Amal Concentric 626 - R302 and I am wondering if this is the correct carb for the engine with the capacity increase.

The bike had stood some twenty years before I got hold of it so with the steel tank sorted & lined and the carb stripped & cleaned I got the old girl running albeit she needed a little sniff of something special but the carburation seems to be all over the place.

So the questions are:-
A/ Is it the right carb?
B/ What would be the best jetting set up?
c/ There is no choke assembly installed in the carb, do I need one?

Please see attached pics.
Thanks & regards, Ken.

[John Wakefield]

Hi chaps,

I have a 1957 20T with a 9E engine but it has a 250cc barrel conversion.

It has an Amal Concentric 626 - R302 and I am wondering if this is the correct carb for the engine with the capacity increase.

The bike had stood some twenty years before I got hold of it so with the steel tank sorted & lined and the carb stripped & cleaned I got the old girl running albeit she needed a little sniff of something special but the carburation seems to be all over the place.

So the questions are:-
A/ Is it the right carb?
B/ What would be the best jetting set up?
c/ There is no choke assembly installed in the carb, do I need one?

Please see attached pics.
Thanks & regards, Ken.

A Its the wrong carb should be Villiers S25
B Jets main 130, pilot 35, jet taper 3 1/2, set out 1.95, throttle slide 3 or 4
C Choke operated by plunger in top of carb or by cable. Choke mechanism is not essential particularly on a trials bike, just flood the carb for cold start.

The barrel is a 34A scrambles barrel which would originally have had an Amal 389 which would be totally unsuitable for trials, the barrel will work OK though with the smaller Villiers S25 carb with the jets as stated above. You will need to make an adaptor up as the S25 is clip fitting not flange.
The 9E engine bottom half serial No 737B was originally fitted to a DKR 'Defiant' scooter

[Spike1947]

Great info.

Many thanks for your input John it's much appreciated. Is the Villers S25 carb still available?
Thanks & regards, Ken.

[John Wakefield]

No S25 not made new, you will have to find a good secondhand one. They come up on eBay from time to time.

[John Wakefield]

Spike, before you go looking for a Villiers S25 you could try & sort the Amal 626. Greeves used this carb on the Anglian so it should work ok on an iron barrel 250.
The jets for the 626 on the Anglian THS & TJS are as follows:
Main 140
Pilot 25
Jet taper .106
Groove 2
Throttle slide 2 1/2

Trouble is that Amal made the concentric 626 configured for 4 stroke & 2 stroke engines, so you need to be sure yours is the 2 stroke variant. Sorry I cant help with that but Rob published some articles in LL's 173, 174 & 175 , Amal Concentric Mk1 A Spotters Guide, well worth a read. If the carb is a 'new build' from Burlin Systems then there may be problems with manufacture as the quality of these has not been good.

[Spike1947]

More great input - thanks

Hi John,
Many thanks for your further input and advice.
Great there is something I can do with the 626, I am aware of the differences between the 4 stroke & 2 stroke 626's so will double check my build and also the current jetting.
I did manage to get hold of a rough S25 on ebay however it's missing the complete slide assy and top caps so I'll keep looking just in case.
Thanks again, Ken.