It's not clutch drag

Ive got a dommie box on mine and it's fine. Is the primary chain adjusted so it not too tight? My clutch wobbles a bit too!

Have you had the clutch off? did you check that there is clearance between the back of the clutch spider and the sleeve gear when the clutch is mounted and the nut tight? A few thou is all you need.

Good point, I fitted a new spider a while ago As mine was rubbing, but to be honest finding neutral when running is also a bit of s knack.

The biggest cause of poor selection with the AMC boxes is probably wear on the bronze mainshaft thrust washer but wear everywhere adds up - the camplate and quadrant bushes are also worth checking.

The best real world test of clutch freedom is to put it in gear, hold the clutch in and try to paddle the bike backwards. If that's difficult then there is too much drag.

The clutch can lift and spin freely but if the spider drags on the sleeve gear it loads the gear teeth and resists free gear movement for the change. Wear on the back of the spider is a clue ,if the inner case is off you can check with a feeler guage there is clearance. As Richard says the Bronze bush/thrust at the KS end can wear and is not obvious.

I don't know about the laydown box, but I had to grind off about 10 thou off the back of the clutch spider on the AMC set up.

On the AMC box you can do it all insitu ,bit dificult to replace the layshaft bearing though. Don't know if its the same on a laydown.