It's been ages since I've posted on this forum so I must apologise for that but I think I might be able to help with this problem.
My poor Huntmaster had serious smoke problems on start up straight after fitting a new barrel and pistons. I did every thing I was supposed to do. I gave it an Italian break in on running in oil and after 1000 miles it still smoked, worse if anything.
It was all down to the rings. The Ariel club have had pistons made by IMD that fit the Huntmaster so I got hold of a couple of plus 20 thou and just put them in, didn't even check anything or even hone the bores. Just chucked them in. Result. No smoke. Fixed.
When the old pistons were in I could kick the bike over and watch the oil pouring down the barrels onto the top of the pistons As soon as the new pistons were in no oil was visible anymore.
The first picture below shows the old pistons with the oil pouring down the bores.
The other is the new pistons fitted.
The other one was me at a rally earlier this year, the talk was getting around I'd bought a two stroke!
Steve