Modern Buddy

Leave my 2t Stella for a week or so and first start appears to be excessive smoke for quite a while. Start next day and back to normal. Is this a common problem due to a leaking bypass ball valve or something?

Could be, or it could be the start of a base gasket (carb to case) leak.

First make sure it isn't a gasket leak.

I found this as well. If I fill the oil tank the whole neighborhood will fill with smoke when I start up Stella.

Now I only top-up the oil tank frequently just to keep the sight glass covered. I don't try to fill the oil tank full.

One thing I cannot find is clear pic in maual or on a schematic diagram of parts or location of ball and spring which I presume it will be when get chance to check once gasket arrives.
Thank you for info

The ball check is under the Automatic Oiler pump cover. Ball goes in first. Then the spring, then a little plastic holder. I wish I took better photos to share with you.

Robot did a nice video on carb overhaul. That should give you a good idea of what you are getting into.
https://www.youtube.com/watch?v=dUDDlGUd1jg

Resist the urge to over-torque the carb base to the engine. There are only two fasteners and it will warp the casting and then not seal at all. An air leak is much worse than an oil leak.

Well thanks all for info I now have check valve and bits filled the oil tank today whilst putting on the fly screen I got. I am going to leave it a few days and use my other scooter and see if the level drops and crack on with the repair.
One thing I did notice with the cap it has a slit in and where it pushes into the tank there is a little pin about an inch down that sticks out. Not sure if this common on all but it catch's little bits of plastic no matter how careful you are lining up the slot so I presume this over time could make its way through and catch in the valve. Just a thought but if I have to remove valve I will pay close attention and report back