My 2T Jonway , a Magnum came with a 19mm TK carb and the air screw was not sealed up like many . Many have 17.5mm or smaller so I was lucky to have a19mm . Mine always needed to give it a sip of throttle to start it up and ran great . Make sure to double check any carb or interest that it has an oil line ( if you want to use the oil injector ) and electric choke as motorcycle types have a manual switch or cabled choke . Mikuni is a great brand of carbs and other fuel parts . Kehin is another good one .
Should you decide to replace the stock oil pump with a ( way better ) Mikuni oil pump you will need to replace the throttle cable with part # 159-26 from PFS . PFS also now sells a Minarelli main jet kit for 15 bucks which is great as most high end part places only have them for Delorto or other expensive brands . My TK uses Mikuni VM11/22 main jets like most and I bought a few from
www.power-barn.com but had to pay per jet instead of a kit and 6 shipping regardless how many I bought .
I always had to give it a sip of throttle to start and more so after I installed a BBK . I replaced the 40 IJ with a 45IJ and now no throttle needed to start . You may want to pour in some SeaFoam to clean out the carb or manualy remove the bowl after you drain it and unscrew the jets to clean by hand with any brand of carb cleaner spray or a stiff solid strand wire . A NGK iridium like BRP8HIX like I use it light years better than the crappy Torch brand that some come with and the iridium is a lil better than the standard NGK . I t will start and run better but no performance gain