Yamaha Pw50 62,5cc big bore kit bogdown Part1

Hello from Greece, I purchased a Yamaha PW50 1992 model for my nephew , and i made some upgrades. I have put a 60cc big bore kit (44mm piston) modified to 45mm piston, so now the bike is 62,5 cc. I have purchased the PW BIG BORE CAR KIT with 21mm carb, Aluminum intake manifold and Boyesen power reeds. When i made the upgrade to 60cc the bike was runing very lean with the stock carburator and also was dificult to tune it due to bad carb condition. When the 21mm carb arrived, i bore the cylinder andput a 45mm piston. I have install the 21mm carb and after some carb adjustments i the bike run pretty good.at full throttle.But i i think that is a little rich from the idling to 3/4 throttle. I have the mixture iddling screw at 1 and 1/2 turn counter clockwise from full closed and set the needle high at the second position from top. Sometimes when the bike runs at high rpms and the kid close a little the throttle and it open it again the bike bog down and have to close the throttle again and wait with the throttle close to decrese the rpms before open it again or the bike will shutoff... Also the bike have about 130 psi of compretion but i have stock exhaust with custom muffler. 62,5cc (45mm piston kit) New crankshaft seals New crankshaft bearings Stock exhaust witn custom made mufler Stock coil Stock cdi 2,5% oil mixing Sparkplug gaped to 0.65 mm I have attached some videos in case you could understand maby what the problem is. In the first video you can hear the bike made two times the cuts off In the second the bike runing good, only in the first 20 seconds you can hear some small cut offs. “Thank you in advance,