and .28 appear identical from the outside.
Many parts interchange, BUT NOT ALL.
tell the difference between .20 & .28
remove the back cover and look at the crankshaft,
.28 is stamped .28 and .20 is not stamped.
came out first then the .28
.20 had a O-ring for a head gasket but this was discontinued
early in the production. The .20 does not have a head
gasket. The .28 uses a head shim.
The only design change was the remote needle.
The .20 and .28 both have 12 head fins and a
diameter of 1.425"