Jet on Amal 389 to BSA Golden Flash

[GFlash]

Hi
Has a Golden Flash from 1954 with 357 cam and open silencer.
Has mounted an Amal 389, which sizes of main jet, needle jet and pilot jet should be appropriate?

Regards
Robert

[RogerSB]

Hi Robert,

As far as I know 1950 - 54 GF originally had an Amal Monobloc 276.

My 1960 GF has a 389 with 1 1/8" choke, 250 main jet, 30 pilot jet, 3 1/2" throttle slide, 0.106 Needle jet, No3 (from top) needle position.

[muskrat]

G'day Robert.
You don't say what size 389 you have or air filter.
With a straight through pipe and 357 cam and a choke size of 1 1/8" I'd start with a 300 main, the rest as per Rogers settings or just a tad richer and go from there.
Cheers

[GFlash]

Thanks for reply.
I have air filter.
Measured and saw that the carburettor is 1 1/8" and the intake is 1 1/16" understand that it is not good?

Regards
Robert

[muskrat]

G'day Robert.
A step like that 1/32" isn't great but it's not too bad. you could use a thick insulating gasket to blend the two together. http://amalcarb.co.uk/phenolic-spacer-26mm.html
Cheers

[Scott and Jay]

Yes, the bore on the intake manifold needs to be increased to 1 1/6 and matched to the carb - if you want to keep that carb. I got a new Premier Amal 389 carb for my 1958 Golden Flash. It as 1 5/32 bore. I got the intake bored out to match this. With an air cleaner but not-too -restrictive Emgo universal mufflers - I had to go up to a 310 main jet. It runs really nicely at that.