DB, my model year 2000 200 HP Johnson only burns 23 GPH at WOT (5800) on my 89 204C Overnighter. I would think his motor should do a fair amount better, like in the 17 - 18 GPH range.
RCORNEJO, I have a Northstar fuel monitor so I have some pretty good numbers for my boat. I think your boat and motor will be a bit more efficient.
At 3500 rpm I'm burning between 8.5 and 10 gph, according to my Northstar fuel flow meter. The variation depends on weight, wind, waves, tide, etc. I average about 2.7 mpg at this rpm range on down to about 2 at wot, about 5800 rpm. Speed is around 26 MPH according to the GPS.
At 4000 RPM I'm seeing about 32 MPH and 2.5 MPG. When I push it to WOT, my Northstar fuel flow meter is registering about 23 GPH and my GPS is registering right around 40 MPH - sometimes a bit below and sometimes a bit over.
Hope this helps.
Gary 93 Gulfstream 89 Overnighter - for sale