Robin 244 knocking (?) after leveling off at top speed

[sbklf]

1980 EZ GO Marathon. The motor is very worn, low compression, not sure about the rod bearings, but it runs very good. Accelerating, it is as smooth as it goes and it sounds good but after it levels off at top speed and runs a bit (1/4 mile or so maybe) it makes a knocking noise. The noise seems to be inconsistant (?). My thoughts are: Rod knock, backfiring, detonation (not sure what that sounds like). Due to the wear, I run about 50:1 fuel. Might this be causing the knock? Any thoughts on how to better diagnose it? Thanks, Kevin

[cart around]

Somebody recently mentioned on here that theirs was also making a noise. It turned out that the bottom skirt of their piston was broken off, and bouncing around inside the case.

[redcloud]

Could be rod as when you take the load off it the engine is bit free'er and good time for parts to rattle. If rod is bad then I would do complete long block kit.
Not to say that when you take off the jug and can do a side to side movement of rod to crank and it seems pretty solid...well you could just looking at piston problems and do an oversized piston/rings kit but for me I would do the complete kit so you are fresh with all.