RGS carb differences

[a101960]

Does anyone know why the RGS according to "BSA twin restoration" book  has three different carb specifications? and does it make any difference?

1962-63      389/80 size 1 - 5/32    main jet 420   pilot 25  slide 3 needle position 2    jet .106

Then for 1962

389/81 size is now 1 - 3/16 and main jet is specified as 440 pilot 30 and slide 4 jet needle is now .107

1963

389/94 size is back to 1 - 1 5/32 main jet 310 pilot back to 25 slide back to 3 but needle jet .104

The owners RGS owners hand book spec is listed as 389/80 size 1 - 5/32    main jet 420   pilot 25  slide 3 needle position 2    jet .106

There must be a reason for the alternatives but in Bacons book there is no explanation.

[JulianS]

Some information on the 1963 A10 Super Rocket, RGS, RGS Scrambler carbs on parts bulletin N8 and also the Gold Star twin supplementary list from February 1963.

These give 389/94 as used on the 1963 USA West Coast Super Rocket and RGS Gold Star twin and 389/81 used on the 1963 East and West Coast scrambler models.

This seems to coincide with the introduction of the 9:1 pistons.

As usual no explanation given in the bulletin.

[Joolstacho]

... And there will be variations re: if/what air filter is fitted.

[Black Sheep]

And don't take the carb settings as gospel either. I tried a 420 and produced a load of black smoke.

[Slymo]

That's substantially larger the the 250 main jet in the Super Rocket. I wonder how they make it drink all that juice?

[mikeb]

Sylmo i think the difference is the presence or absence of the original filter. the US bikes had filters (for all the sand and dust) and a smaller jetting; the UK bikes had no filter and larger jetting. my 61 super rocket being UK origin had a 420 main on the 389/46 (but actually runs better with a 440 on a new 389 even with new style cone filter fitted). i think those numbers in the book are a starting point to tune from.

[Slymo]

Mine is an ex US East Coast bike with a pancake filter so that makes sense although that's still a big difference. I've set mine up to book settings and it seems to be good even with the muck they sell us at the bowsers here in NZ