Did you accidently charge the battery with backward terminals ? Did you install the battery in a reversed position ? Plus post is now where the minus post was ?
Just remember that a prop and exhaust in FOWARD are pushing SOLID water.
In REVERSE the prop is spinning in a MASSIVE CLOUD of exhaust fumes. NO hp is needed when boat is floating.
Ignition appears to be good.
I like the EXHAUST FLAPPERS stuck somewhere.
I used Seafoam about 1 tankful a month got 12 % better mileage.
Also tried the Honda way. Run 15 minutes at about 60 mph. Got back the same mileage. I do this way now.
DUUUHHHH
The....U S Government..... SPECIFIES what goes into motor oil for cars !!! They also specify what goes into gasoline grades for cars !!! If they did not ??? DEAD cars by the millions.
SUPER DUPER additives are all FEAR B S.
Use 2 props. 1 for light load. Other for a crowd. Go to 4' of water. Jump in and change the prop. Havs spare nut and washer if needed. Been there many times.