I put a 21 J carb off an OS 28xz on my .25.
And it tunes just like a normal engine (tune HSN 1st then do the LSN), not the Go tuning way.
I had a lot of trouble with the Go carb, lean bogging and air leaks around the carb throat, had a spare OS carby lying around so I thought I would try it out.
I'm very happy with the way it performs now.