anywhere near the top end of the carb circuit the engine dies away with popping and banging in the exhaust. went to a manual mag thinking my ignition timing was at fault . then tried carb settings. i have gone from a 380 , 330 and now 280 main jet and its almost perfect. 260 is probably on the money. very near to book settings for road rockets and early s/rockets. i have an ally head with bellmouth . 1 1/8 mono ,2 into 2 exhaust.
where have these big main jet sizes have come from ? 420 main jet is massive.
now , i only need to set up motorway cruise jetting.