I put velocity stacks from
http://www.cbperformance.com/ on my 44s. I find that the engine runs smoother with them on-not too quantitative, just one of those 'feelings.' It's also easier to balance the carbs with a unisyn gauge with stacks. The stack helps to collimate the air before it enters the carb, and I think supposedly to speed up the air a little. There are tall and short stacks, so be aware when you order. You want 2 1/2 to 3" stacks if you run a standard 3 1/2" tall filter. They are cheap, and easy to install.