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B40 star best set up for wrong carburetor

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My 1965 B40 has a Amal 627 (428) concentric carb. 20 years ago Dave Smith of BSAOC said its from a Trident but is ok and recommended the set up as:

Main Jet: 140
Pilot jet: 20
Slide 3
Needle position 2
Needle jet .106

( I don't actually know how its set up)

I notice that the concentric that was fitted on some later B40's was a 626. So was Dave Smith right that my 627 as set up above should be fine. ?

I am presuming after 18 years of doing nothing in a garage I'll probably need to check/clean/service it. I did take it apart once but only checked if for crud & cleaned jets ( oh yes then had to emery the flange flat that my make over tightened).

I will see if I can the bike going, but would be useful to know if the 627 should be ok.


Your bike would have had a 1 1/16 inch monobloc, about 27 mm bore. The 627 is also 27 mm bore.

Condition is important.

Lots of information on the Amal website including rebuilding the Mk1 concentric, see link;

Also see the tuning guide,

You should find all the information you need and you will be getting it from the manufacturer.

The 627 concentric has no air slide ( or at least the one I have doesn't). Previously I bodged a choke for start up with a perforated cap -  I had no air filter attached- just removed cap when warm.

Is there any off the shelf or tidy bodge to fit an air filter with a choke ability ? 

[I could just buy the  the right carb and an air lever/cable, but if I can reuse what I have i'd prefer to  if there is a sensible fix ?]


Often bikes will start with just a good tickle of the carb and without a choke. Have you tried this?

But if you want a choke why bodge it, why not just fit a choke slide, cable and lever to your exsting carb.

It will be interesting to see how your concentric carb set up compares with that of Phil C in the other B40 post!


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