Has anyone suggested the possibilty of a cracked fuel feed line? Several times I have found a cracked fuel line often right at a fuel connection nipple. They are often difficult to see so pull and bend a little on the fuel line at each connection while looking very closely for a break in the line, or just replace all the external lines including the one that runs from the remote needle valve to the carb. OS 40 LA's are normaly EZ to start and keep tuned, very user friendly. I also had a time once with a 65LA that a Great Planes remote fill valve would fail to pop closed after fueling and I couldn't draw any fuel to the engine (not the engine's fault). If you are using a fueling valve on the plane, check that too.