Re: Motor running faithfully now, but.......
You may be building up some black stuff in your exhaust. I opened mine up it's louder but man it picked up some power.
Still. I rarely go over 15 mph on my china engine MOOP2 bike.
Another little trick is to hold down the tickler in your carburetor till gas leaks out then let go of the tickler. This gets rid of air bubbles in your fuel line.
It's little things like that that makes a world of difference in these things.
You have found the fountain of youth. Ride and forever stay young.