Has anyone been running a K&B sportster .28 Are you able to run it stock with the venturi and nva assembly that it comes with?  Mine is not running well in stock form. I think the venturi is way too big? I did get a good answer about this on Stuka stunt but wondering if there are other answers as well since I only got 1 reply.

Measure the venturi diameter with a calipers or even by just trying drills of different size to estimate it.  For C/L sport flying it should be under about .285 with the typical OS or Super tigre style needle valves.  If the motor can't be adjusted to run rich with the nose pointing straight up the venturi is too big, or there are leaks in the the fuel system somewhere.

I had several K&B 28's.  They ran just fine although many of them a needed a long break in.  The aluminum sleeve and iron coated piston don't  wear as as fast as iron on steel or aluminum on chrome.