Good afternoon. I hope I am posting this correctly. I have a 1978 Bayliner Admiralty Fisher with a Volvo 270 and AQ 120 or 140, not sure. Can't find the data tag. Anyhow, it has two Solex 44PHN-3 carburetors on it and one is non rebuild able. It seems as if I would having better luck finding a unicorn guarding a pot of gold at the end of the rainbow. I have heard that it is possible to upgrade this setup to a downdraft twin carb setup and changing the manifold. What do I need to get? I am finding twin carb Volvo setups with manifolds fairly reasonable on ebay. I just need to know what to get. Thanks. Also, what is the difference between the B 20 and B21 engines?