Re: My MB runs very well after 2nd run...
The sympton you describe can also be a result of the fuel tank not venting properly. This is a common problem and can be traced to the fuel tank cap. To eliminate or confirm this try riding with the cap loose. If the problem goes away, you found it. If venting the tank doesn't help start with your wiring making sure your connections are good and not vibrating loose. Let us know what you find.
Any good air cooled 2 cycle oil will work and we suggest breaking in @ 24:1 then moving down to a 32:1 mix after a few tanks.
Tom
Tom