Frank-
Brown may have made two sizes- measure the bottom throat- the original Fish was 1 1/2" dia. The Tyce version is rather interesting. It uses a fixed inlet jet, and a grooved plate attached to the choke shaft rides over it. A parallel linkage between the choke shaft and the butterfly shaft synchronizes the metering plate with the butterfly angle. There's also an airbleed screw that regulates fuel flow- a more easily adjustable way than removing tiny little shim washers from the metering screw in the fuel pickup arm. If you attempt to alter the factory setting of (2).010 shims and (3).003 shims, you would be wise to have replacements on hand. It's very easy to drop the screw (brass, nonmagnetic), and lose one or more shim washers FOREVER. Also, there are two Arm shim washers in the carb body that space the fuel pickup arm- don't lose those. Check the play in the throttle shaft bushings by wiggling the arm- if the arm sticks at any point, they're probably worn out. My M2 has this problem, so I have to figure out a fixture to install new ones. The inside end of the bushing is machined to the same 1 1/2" radius as the bore, and has to go in so it's perfectly aligned with the wall of the bore- that will be a neat trick! Where did you find the Brown carb?
