get a 14a or 15a exhaust manifold and a 14a or 15a carbie 2

Do you mean A12, A14 and A15? 12A is a rotary engine.

The A14 and A15 use the same carburetor type as the A12, Hitachi 306 with same size throttle bores. The jetting is different.

Have these parts made your A12 engine run better? Are the exhaust manifolds bigger?

this is something i have just discovered also, the stock a14 and a15 (not sure if its all models or just some yet) but they use a bigger exhaust manifold, it looks heaps better for flow than the stock a12 ones, and doesnt have that carby heating thingy ontop of it, will get piccies soon