Different bore and stroke Slakey 54x54= B.....56x50=A.
Arhhh Ok so one needs to swap the engine, does the A corner better? And is that because of the frame or throttle response?
When the track gets rough ( Old School rough) the B suspension will be an advantage
but on todays VMX tracks i think the A is a better option .
The A really revs out ( i compare it to an RM 125 S with an extra gear ) the B you have to short shift , if you try to rev it out it signs off real quick .
The RM 125B is a great bike i just prefer the slightly lower ride of the A and the A motor characteristics .
If you get a chance ride Joans 125 A /B hybrid its a really great ride
Next favorites for this class would be
RM 125 B
RM 125 S
YZ 125 X
YZ 125 D
I have not cut a lot of laps on the 76/77 CRs but the ones i have were a good ride and very competitive .
I think a blinged up CR is the best looking bike for the era followed by the RM 125S and the RM 125 B