James,

Looks like no one what's to say anything so I will give it a go. There are many theories and IMHO the following have substance.

1) Engine runs cooler because heat gets carried away easier
2) All other YS engines have fuel delivered into the crankcase after it has been metered by the carburettor and before it is forced into the head. Keeps bottom end cooler. In the DZ the fuel goes directly into the head so the engine relies on blow-by to adequately lubricate the bottom end. Other words the thinner the fuel the greater the blow-by.
3) Better fuel atomisation because of the thinner oil means you get a better combustion.

I have tried both thick and thin oils in this engine and I can tell you that the thinner oil is much better. Engine runs smoother, more power and more fuel efficient.

Wildcat I believe supply a DZ mix with uses low viscosity oil from Klotz. Give that a try.

I mix my own DZ fuel by mixing Klotz KL-198 LV with some Klotz KL-200 HV to increase the fuel viscosity slightly. I do believe KL-198 LV is a little too low in viscosity to give my engine the protection it needs. I swear by this mix at it is cheap compared to other alternatives. 25% nitro and a squirt of Armour-all completes the cocktail.

Peter