Is it straight gas (petrol)? Or does it have ethanol mixed in?
In the former case, maybe. Might not even need an additive. In the latter case, I'd be skeptical; none of the additives available here that I tried were worth more than about 1 month.
OTOH, that was in a 1-cylinder, 2-stroke, low horsepower carbureted outboard
. Perhaps a two- (or more-) cylinder higher-displacement motor
, and/or perhaps with fuel
injection, the outcome could have been better.
How many gallons or liters, depending on where you are? Most old gas (petrol) will run through cars relatively easily...