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Posted by JOHND [12.27.101.218] on Monday, May 09, 2011 at 08:14:23 :
In Reply to: Stromberg BXV-3 Air/fuel mixture posted by spencer Chance [68.226.140.116] on Sunday, May 08, 2011 at 23:59:06 :
Remember that the butterfly regulates the amount of air flowing into the carb, and the flow of air draws fuel via the venturi effect. If it's true that the engine would over-rev as you say, the lack of air is not the problem, the excess of fuel is the problem.
I would suspect that the float valve is not shutting off, and the bowl is overflowing into the carb. When this happens, the venturi effect goes out the window, and the fuel pump pressure forces fuel into the throat of the carb regardless of the butterfly position.
I also have the Stromberg BXV-3. The fuel inlet fitting into the carb is also an orfice and the valve. Take the fuel line off, remove the brass inlet fitting into the barb and study it to see if the needle is seating correctly. Also check the float to make sure it hasn't sprung a leak allowing fuel to fill it up and cause it to never raise and operate the valve.
Good luck with it.