It’s what you cannot see that will starve your outboard for fuel!

It’s what you cannot see that will starve your outboard for fuel!
This is a fuel filter from under the cowling of a Mercury four-stroke outboard; note the particulate matter that drained from it.

Today's outboard engines are equipped with multiple filters to catch tiny particulate matter that passes through the boat’s fuel system. The boat, when rigged correctly, will have a 10-Micron fuel water separator filter mounted between the fuel tank and the engine, before the primer bulb. The filters under the cowling on a four-stroke usually consist of the low-speed primary filter, a high-speed filter after the engines fuel pump, a filter located on the high-speed pump within the vapor separator tank (VST) and possibly one additional filter located just after the VST. There is also another filter inside each fuel injector. The purpose of all these filters is to catch, or I should say to attempt to catch, as much trash as possible before the fuel enters the engine through the fuel injectors. Two-stroke engines will generally have a single fuel water separator filter under the cowling as well as filters in each injector.

The reason for so many filters is that ethanol can encapsulate trash and pass through a filter, and so a series of filters is the best defense against engine damage. All fuel water separator filters should be changed once a year, and I prefer twice a year as filters are cheap. Carry spare filters on the boat and a filter wrench. Under the cowling filters on a four-stroke outboard should be changed once a year or every 100 hours of operation. 

Have a safe and happy summer season,

Chris Mapp
Coastal Bend Marine | Port O’Connor, TX | 361-983-4841