1956 A10 RR Amal Carburetor recommendations

[thackero]

I have a 56 A10 RR spec with alloy head. It was fitted with a 389 Amal monobloc however it would seem that a 376 may be a better option. I know the original spec was a TT AMAL. I am going to purchase a new AMAL carb so my question is should I buy a 389 or a 376 ? Engine has a large journal crank, alloy head and standard pistons not HC. Thanks

[Rocket Racer]

What's the port size into head? The 376 was typically 1 1/16" (27mm) , whereas the 389 was 1 1/8" (28.5mm) . I doubt it'll make much difference in practice. The 56 TT carb spec was originally an 1 1/16"  so the smaller 376 is more consistent size wise if the heads not been ported further. My suggestion is the 376 if your head is still 27mm. these were fitted in that size to the 56 GF.

I'm just in the process of rebuilding a 54RR with the orig TT and considering modifying the slide so that it idles, something a mate did. ,
For a typical rider I dont think the carb size matters that much in the range you're looking at. Smaller carbs set up comparably as a generalisation respond better at lower throttle settings, while big ones are better for go fast riders.

[Black Sheep]

I have a '59 Flash with a RR head and 357 cam. Carb is a 389, main jet 300. It ran for years on a 280 main jet but even running E5 petrol it turned out it needed a bigger main jet. It goes well, just as happy as 20 mph as 75 mph on the motorway.
I don't suppose it really matters in the real world whether you fit a 376 or a 389. An iron head Flash on a 376 carb and 356 cam goes pretty much just as well as a RR.