Hello everyone. I know there are lots of experienced outboard people on here, hopefully someone can help on this one. This is a '77, 70hp evinrude. When accelerating the engine bogs, if you hit the choke it will pick up and go (which tells me it's running lean). The guy who has worked on it has cleaned the carburetors, set the floats, checked the compression (100psi on all 3), cleaned the fuel tank, replaced the fuel lines including the bulb, cleaned the filter screen, rebuilt the fuel pump, and installed new spark plugs. After all of this it still does the same thing. Now he is saying that it is sucking air around the butterfly shafts on the carburetors, before i buy carburetors i thought i'd post on here to get some ideas. Any and all help will be greatly appreciated. 