In the "day", the 15/16" (actually .954) Mac flatback was the carb of choice for the warmed-over 580, as well as for other engines. They' are a little harder to find diaphragms and gaskets for than a Tilly, but they are availble if you dig. They run and tune every bit as well as a Tilly, too. I can't wait to try my two new ones on the 101/Mc20 "clone". TJ
tj thats kinda funny .!!! i was telling sterling on the phone awhile ago ...how many west bends i have with flatbacks .. i like the dang things .if they will run on an mc49 and other mc motors that are twisted to 9 or more .!! im pretty sure thery are just fine for any 580 ..
hhhmmmm mc101/20 clone .. ?? is that like my mc70/49 class motor . i learned one thing in a hurry ...when you weld the top half of a std series side cover to the bottom of a super series side cover they weld terrible ..but i have some secret rod that works perfect ..
Steve, when I built the Swoopster I was heavier than I am now. I wanted more torque thai I could get out of an Mc20 or Mc30. We had an original series 101, Siamese ported and only .010 overbore. I found an Mc6 round head, put Mac 20 shrouds on it and a Hovey dual intake with flatbacks. It looks pretty close to a real Mc20, and has the extra power I needed. The only issue was turning the Hovey intake into one that fed both carbs into the reed opening. I also took out every other reed separator rib and water jet carbon fiber reeds to work with the 4 reed openings instead of eight. TJ
Your 580 probably came with an hl 88 which I think was a 5/8 venturi carburetor. It also came with one of the worst intake manifolds imaginable. The reeds are tiny, and there is no stuffer on it. The perfomance gain of a bigger carb won't be noticable. An aftermarket intake, and some porting are what you need to wake that thing up.You can get it to run with a Mac 6 but that would take some parts that would be really hard to find. A breathed on Clinton will out-run a stock 3 port.