Fuel & Fuel System Frequently Asked Questions

What is the proper break-in procedure for 2-cycle, 4-cycle, and OptiMax outboards?

Break-in is important to ensure correct engine performance and life. Follow the procedure listed in the Operation, Maintenance and Warranty Manual.
Generally, for the first two hours, we recommend avoiding extended idling, sustained periods of wide-open throttle, or holding the engine at one speed for extended periods of time. New two-stroke engines require additional oil, either through the addition of oil with the fuel or programming inside the computer. Four- stroke models DO NOT require additional oil added with the fuel during break-in.
Break-in procedures are described in the Operation, Maintenance and Warranty Manual supplied with each engine. Use the "Operation & Maintenance Manual" link page if you need to find/print a replacement manual.

My engine keeps stalling at idle, and I find the primer bulb soft. Why?

Several basic items should be checked. First, is the fuel tank full of fuel and vent open? Second, is the fuel line pinched from a heavy object sitting on the line, or is a tight connection restricting flow? Are there cracks in the line or connections, allowing air to leak into the fuel system? Finally, due to the changes in fuel composition, have your dealer inspect the fuel pump check valves for cupping and replace the primer bulb with the latest style.

What octane rating should the gasoline that I use in my motor have?

United States and Canada
Use a major brand of automotive unleaded gasoline with a minimum-posted octane rating of 87. Leaded gasoline is not recommended.

International
Use a major brand of automotive unleaded gasoline with a minimum RON* octane rating of 90. Leaded gasoline is not recommended.

Performance Products will have different requirements, consult your Operation, Maintenance and Warranty Manual. Use the "Operation & Maintenance Manual" link page if you need to find/print a replacement manual.

RON : stands for "Research Octane Number". If the RON is too low, acceleration knocks occur (these are usually audible)

What can be done to maintain fuel quality during periods of storage?

Mercury Marine recommends the use of a fuel stabilizer to prevent fresh fuel from undergoing degradation and oxidation during fuel storage. Mercury offers Marine Fuel System Treatment and Stabilizer both under the Mercury Precision Parts or Quicksilver brands. Additional benefits of the product includes: easier engine starting after periods of storage, elimination of the necessity to drain and dispose of fuel, prevention of the formation of deposits that could clog filters and tiny passages in the fuel system; and elimination of corrosion and rust throughout the fuel system. It absorbs water and prevents fuel line freeze-ups.

How can I lower the possibility of water trapped inside the fuel system being drawn into the engine?

The first issue is to prevent the water from entering the system. The second is to determine how much is in the system; if over a quart, you cannot effectively eliminate the possibility without draining the tanks.

If the amount is small, Mercury offers Marine Dri-fuel both under the Mercury Precision Parts or Quicksilver brands. Dri-fuel and Marine Fuel System Treatment and Stabilizer are designed to absorb water, allowing it to pass through the engine.

Mercury Precision Parts offers other alternatives, water separating fuel filters and a Water Eliminator. The Water Eliminator uses polymer crystals encased in a plastic filter to absorb water from the fuel in the tank. It is supplied with a 2 ft. (610 mm) lanyard and is designed to drop into the fuel tank through the fill. You will need to check to ensure that your fill hose routing is straight; excessive bends will not allow the Water Eliminator to reach the bottom of the fuel tank.

How do I connect my kicker motor to the boat's main fuel tank?

First you must determine if both engines require the same type of fuel supply. Generally all four-cycle and larger two-cycle (oil injected) outboard engines require straight gasoline. Smaller two-stroke outboards may require a gas/oil mixture and will experience engine damage if operated on the straight gasoline used with larger engines. In these applications, two separate fuel tanks are required, one for straight gasoline and one for the gas/oil mix.

Two preferred methods are available when both engines require the same type of fuel. First, use a fuel tank with dual pick-ups, one for the main engine and one for the kicker engine. Both engines will have separate fuel hoses and primer bulbs. The second method requires a 2-way fuel valve, located between the primer bulb and engines. The fuel line from both engines is connected to the fuel valve, which is rotated to deliver fuel to the appropriate engine.