Actually the problem is one carb. Like I said each cylinder needs to be set a little different and using two carbs allows you to do that. Nothing man made is exactly the same and that includes model engines. One cylinder will always run a little differently needing a different fuel mixture. Just exactly the same as several engines of the same make and model; say 5 Saito 65 four cycles. No two of them will have the same needle setting because each is a bit different. Just like the two different cylinders on a twin.

That is exactly what Gen Saito said when he gave me the twin carb set ups. I would think he knew what he was talking about. He made them.

One other thing, You said that the original twins didn't have the pump but the ones I bought were the first released in Japan, released before the ones in the US, and they did and according to my friend Ewasa, who owned the local shop in Sasebo, they always had the pumps.

I have set up an OS FT120 to use two carbs and the difference is night and day. One cylinder is always a bit different than the other and using two carbs can solve the problem. It works, I've done it