Front brakes is bent disc
Black smoke at high rpm is excess fuel unless it's high altitude only then needs rejetting
Chain stretching can be rest sprocket wear - a set with chain is about 50¥ but mine needs loads adjusting and I need buy some proper chain lube of taobao at 20¥ a tin
Can try get DID O ring chain which is better
Don't bother with only chain no sprockets poor choice there
I have a CG150 motor I have 15 T front 43 T rear and think it's the limit
Check and replace steering head bearings but these are shit design just bike ball bearings 10-20¥
Head light let me know as I have issues with seeing at night and assed off already haha