I knew there was a reason I like premix!
Other thing-you said "first time out" .... Did you have a smaller boat before and are you using it's fuel tank?
I had that very problem a few years ago when I swapped my tank from my old Suz 25 to my "new" Yam 55.... I couldnlt run > 4000 rpm or it died of fuel starvation. The Suz was running a 1/4" fuel line - fine for 25HP. problem was the fuel pump on the 55 couldn't overcome the friction of dragging the extra fuel through a few feet of 1/4" line.
A few quid for new 3/8" hose, primer & connectors and never had a problem since.