Fuel consumption for dt4 2 stroke?

[grplans]

Can anyone advise what sort of fuel consumption a DT4 2 stroke should be returning on the recommended 1:100 mix? I've bought this engine second-hand and only have the internal tank - wondering whether it's worth buying the external tank and lead (I think part no DT4Z?)

[boats.net]

I don't have those specs on that engine but would guess it's about .5 gallons per hour at wide open throttle with heavy load.