what type of gas consuption should i expect of my 1996 johnson 90 hp motor. i use it for lake fishing only. I run back and forth to fishing spots then do several hours of trolling at idle speed.
The "rule of thumb" for outboards is GPH = 10% of HP at wide open. Approximately 9 GPH for yours. This will be ball park and of course you'll have to carry spare fuel until you get a good feeling for what your engine actually does. Trolling? I don't know, but it will be a lot less .