1990 Yamaha Outboard Question

I have a 150 Yamaha, and recently I have replaced a coil due to a dead cylinder. The syptoms were I was only getting about 4200 RPMs. Well, after I replaced the cylinder she ran like a top at 5000 RPMs. Well, right here recently she is doing the same thing. But, this past weekend I let a friend borrow the boat and he ran the tank dry. But she is displaying the same syptoms as the dead coil issue. Is it possible that I have a fuel delivery issue? I put brand new NGK plugs in her and fired her up and ran it. Well, for the first 200 yards she ran like a champ at the correct RPMs, then the same 4200 RPM running. Anybody ever dealt with this????