You certainly don't need a jet anywhere near that size to feed a 150cc scooter. You must have some major air leaks between the carb and the head.
I run a K&N cone filter on my scooter.......stock exhaust.....and a 115 main jet is just right. I don't care what you have done to your exhaust....it will not require as big of an increase in jet size as you have already made.
I have a two cylinder motorcycle, with a separate 32mm Keihin Carb for each of it's 375cc cylinders. Came with conservative 125 mains.....I have upped them to 135.
My 400cc Yamaha ATV has a Mikuni 33mm carb.....it has a 112.5 Mikuni main jet, which is equal to a 128 main in a CVK, or Keihin carb.
Better check that manifold and such.
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