C = 30mm carby.
X = 34mm carby.
The next few models all had 32mm carbs which should tell you something....
"Barrel sizes"?
All had 56mm bore, at least until the 1986 S model. Yamaha does over-sized pistons in 0.25mm increments up to +1.00, and Wiseco do +1.50 and +2.00.
The C and X barrels are interchangeable, provided you have the intake boot to match the carby.
The X barrel has a reputation for being very peaky.
I cannot confirm this, 'cause my X has a ported C barrel on it, so I don't know what a standard X is like....
My (standard) C is pretty much as you'd expect from the specs and the era - doughy down low, strong mid range, good-but-not-great top end.
In comparison, a standard D has more everywhere, esp the top end.
FWIW, compared to the C, the modified X has marginally better bottom end powe, HEAPS more midrange, but falls flat on its face in the very top end - it is a much faster and easier to ride bike than the C.
