From all of my comparisons - ZDZ has the best - smoothest 60-80 singles on the market .
best in price -
best in smoothness
best power per displacement
best carb setup - -rear induction rotary valve.
Longivity? properly maintained, as good as any - we now seen engines with a few years on em with no power losses thru wear and they
have hundreds of hours on em .
By the same token- I have seen em ruined in a week---
My point here -is that given proper care -- these engines are as good as any- better than most.