Have just spent a lot of hours playing around with b12 carbs on a 1127 power screen engine with a full yoshimura system, might not be the same for all, but I ended up with standard b12 carbs apart from having dynojet stage 3 needles and springs with needles on top notch 2 1/2 turns out on mixture screws 160 main jets. Runs really good, my needles were second hand so may have been a little worn, polished them up with some scotch brite which made it run a lot better mid range. Made just over 125hp on the dyno but that was with 155 mains and it was flating of at the top end hence the 160 jets.