Sorts of Ports
I am installing new pistons in a 1972 Yamaha CS5 electric-start 200. On the intake side of the pistons, there are two oblong ports that line up with two "troughs" cut into the cylinder wall. These troughs aren't tied to the transfer ports, or anything else, so what are they for: to create turbulence in the air/fuel mixture, or to relieve pressure above/below the piston somehow? The ports in the new pistons are measurably smaller than the ports in the old pistons. I don't know if enlarging the ports is beneficial or necessary. I'd like to know what they do first.