Tao Tao DB-10 and DB-14 issues

[PleaseW84myRX8]

Just bought these two for my kids and have some oddity questions and some actual maintenance issues.

Issues with the DB-10:
If I sit on it (I'm 165 lbs), the bike won't move and bogs down when I try to ride it. I wanted to teach my son to ride it while I was on the back, but it won't move and when I try to accelerate, it just bogs and shuts off. It seems to know when the compression of the springs occurs and starts to cut fuel or something. Not sure how to address this. Never had this issue on any pit bike before. Once he starts to learn and gets into rough terrain, this can be a major issue.

The automatic transmission. How many gears does it shift through? I tried getting my older son on it, and I listened as he drove in circles and it didn't seem to ever leave first gear, and he was moving slowly (like, I could jog next to him), and the engine was definitely at high rpm. Can I get some help with this?

. It will make a sound like the engine is scratching or rattling. It seems to be constant. You can hear it pretty clearly. I know these engines are cloned from Honda engines, but I've heard no Honda engine sound like either of these two TaoTao's and am concerned.

Issues with the DB-14:
The bolt that holds the fork onto the chassis of the bike seems to be stripped. Or I don't know how to tighten it. Both bikes had an issue where the front wheel would constantly loosen and point a different direction from the handlebar position. But the 10 was able to be tightened for now. I couldn't tighten the 14. It just kept spinning and quite loosely, I'll add. The bolt size is different, so is it supposed to be tightened from the bottom? Before I start taking it a part, I'd like to get some info on that. I had my torque wrench set to 15 pounds so it shouldn't have been too much for it to have stripped unless these bolts really are just THAT cheap. If I need to replace it, can you recommend something that is stronger so this won't happen again?

and listen to the sound. It sounds as though there is metal scraping occurring at moderate to high rpm. It is kind of hard to hear with the cell phone camera, but in person it is very loud and noticeable. It comes in quite clearly at :06 - :10, though. I have had many bikes in my time, but never heard a bike sound like this.

Lastly, both bikes have two issues. The first is that fuel seems to leak from the carburetor. How do I fix this? I've tightened the clamp and the hose, but still they leak. Second, both engines will only run if the choke is in this position (see attached image). If I move it up, whether the engines are hot or cold, the engine will immediately start to choke and die, as though fuel or air was not getting into the system. You can also see the leaking at the bottom there. Just want to confirm, this IS the choke, correct? Is this the correct position then and I should just ignore the "up" position?

Other than this, we had fun on our first ride. But would like to have a longer ride once these issues are addressed.

(also thanks for reading my lengthy post)