I've been working for a few hours trying to tune my friends 1904. He's running dual 36 dellortos. The issue I'm having is with the mixture screw on #4. When adjusting all the way in/out, it doesn't change the idle speed of the engine in the slightest. With 1-3, when the mixture screws are turned, idle either drops or increases (to a point).
We pulled the idle jets, cleaned them out, cleared the carb body (with air), cleaned the mains, replaced the rubber washers on the idle stacks, and still nothing.
I thought it might be a vacuum leak, but was unable to locate one.
Totally stumped, and looking for suggestions.
Thanks!
Fred.
