I would suggest the carbs are larger than 1 3/16 to achieve 149 mph . Factory records only record ,hopefully accurately what the bike rolled out the great north road door with ,not what transpired later . Ie Marty's blue bike left the factory as a rapide , Mr Vincent supplied straight through pipes at no charged as acknowledgement of Marty's promoting the brand etc etc
Photo of the Day John Edgar / Rollie Free Prototype Black Lightning II
32 mm TT Amals according to info from Big Sid's book........Probably the biggest carbs available then........not too many big capacity engines to use massive carbs back then..........engine only pulls less than 6000 rpm max so no big demand there.......Dont forget the Horners got 96 odd crank HP from their Goodwood bike back in 2014 and that had 1 3/16" Mono blocks on it.