Suzuki 2 Strokes

Guys, having sorted out the none starting (see my other threads) and got the engine running, I find that as the engine warms up, it has a heavy rattle/knock at tick over. (no knock when cold). The noise disappears as the revs increase although does reappear during odd times whilst riding as the rev rise and fall. Once on the move, the bike performs rides well. The bike has just been re-bored and fitted with GT750 pistons 9less than 100 miles) . I am no expert but my guess is that this is "piston slap" or perhaps something loose in the engine = it appears to be from the middle of the left cylinder. thanks for any suggestions

Sorry, don't really have an answer. Is timing set properly? If running points,there condition?
You could pull head and see if piston rocks in bore. I would hope not after rebore,but ?
You may want to remove cylinder and check bore measurements are not to loose or tight,again I hope not.
If I'm not mistaken, the piston crown and skirt will expand with heat, this is why the piston should be measured in the area of the pin.