It's probably due to high compression. My 83cc BBked 139 engine bike became super hard to start after it finished it's break in. This is not unheard of with BBKS, chances are you require an additional head-gasket. I added two additional gaskets and problem solved.
However the proper way to fix this is to have your engine and head milled by an automotive machine shop. Using multiple gaskets as spacers is a bad plan, and will lead to head leaking down the road.
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2011 Roketa MC-23-150
4T 150cc 157 qmj
24mm carb w 115 main jet and paper cone air filter
Manual petcock w Tygon fuel lines
Scrappy Dog Scooters Retro-slash stainless straight-thru exhaust
RED spring clutch
Adjustable CDI (brand unknown, it's blue and red and works great!)
KOSO high performance variator w 12g sliders
Gates Powerlink 835-20-30 belt
GPS verified 65mph on flats.
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