Outboard motors are very expensive to replace not too mention everyone wants the maximum performance too. As a tournament angler and guide I spend many hours on the water and consume lots of gas. Most gas these days may contain E10 in it which is a strong water absorber that attracts water into gas. E10 gas has a maximum shelf life of only 3 months under ideal environmental conditions, and can absorb excess water into gas in only a few weeks or less. Only 2-3 teaspoons water/gallon will phase separate E10 gas. Ethanol blends absorb 40-50 times more water, compared to 100% (non-alcohol) gasoline. Marine engines and engines that have a vented fuel system and those that reside in humid environments have the greatest risk for E10 water contamination. Explore the many different stabilizers or water removers out there to combat this problem. Star Brite has a complete lineup
Octane boosters are another great way to up your fuel economy and performance of your outboard. There are many different brands out there to use. I trust Amsoil products in this area. Star Brite is another company that makes different kinds of fuel treatments to ensure maximum performance and longevity of your outboard.
Another area to focus on is the proper oil whether you are running a 2 stroke or 4 stroke engine. I run a Mercury Pro XS and only use the DFI optimax oil. You can also use the Premium Plus 2 cycle oil but you will affect overall performance of your engine. Make sure you are running the correct oil for your engine and spend the extra dollars on the best. It will pay you back ten fold some day.
Lower unit oil, spark plugs and props are the last areas to address when getting the best performance. Make sure you are using a synthetic oil in your lower end. Check your and treat your spark plugs at the end of each season. Explore options on upgrading your plugs. As for props, there are many types and styles out there. Remember, you don't have to re invent the wheel, the internet has tons of information that can help you get the most out of your favourite outboard. Star Brite products are available at Canadian Tire.