
During certain conditions, any marine vessel can experience a vapor lock. Vapor lock occurs when the fuel in tanks, lines or carburetors reaches a boiling point that causes vaporization inside a confined space, such as a carburetor float bowl or fuel lines. Heat, and in some cases the grade of gasoline used, causes vapor lock. Vapor lock can be recognized by certain negative engine performance characteristics, which include hard starting after a "WOT" (wide-open-throttle) run, hesitation and stall upon acceleration, overheating due to insufficient cooling and pinging or knocking. Preventing vapor lock involves some inspection and possibly retrofitting some of the vessel's on-board components.
Instructions
1 Consider whether you use gas that contains heavy amounts of ethanol (a gas oxygenator), winter-grade fuel or additives that contain alcohol in your marine engine. Alcohol leans out the properties of fuel, leading to a lean mixture to the carburetor. Leaned carburetors allow the engine to run excessively hot.
2 Buy only small quantities of gasoline that you will use immediately. Store extra gasoline for no more than 90 days. Do not use any gasoline stored for more than 90 days. Dispose of old gasoline or gasoline that has a pungent smell of varnish and gum. If you have gasoline in the tank that has high ethanol content, purchase high-octane gas to add to it, and use the high octane blend until you purge the tank of the old fuel.
3 Avoid using fuel that has a Reid vapor pressure rating between 11 RVP and 15 RVP. Switch to a fuel that has 8 RVP to 10 RVP. Consult your owner's manual for the recommended octane and RVP-rated fuel for your craft.
4 Inspect all of your fuel lines and hoses for evidence of sharp bends, kinks, cracks or loose fittings. Replace such lines and hoses with those that have smooth-bore interior lining, that have the correct pressure rating and manufacturer's recommended diameter.
5 Measure the circumference of fuel hoses and lines with a tape rule. Divide the circumference by 3.14, then subtract the hose lining thickness. Small diameter lines and hoses cause restriction.
6 Use your hands or an end wrench to loosen and remove your water separator bowl and dump the sedimentary water. If the fuel filter has not been changed according to recommended intervals, replace it with a new cartridge, using a filter wrench to remove it. Screw the new filter on by hand. Use an end wrench to unscrew the brass inlet fuel line connection at the carburetor and check the cone or filter screen for clogs. Clean or replace the in-line fuel filter.
7 Check the engine cowl (case cover) for clogged vents. Make sure all the engine cowl vents are opened and unobstructed. Replace the air filter or spark arrestor if it appears clogged, oil-soaked or deteriorated. A clogged air filter or spark arrestor disallows cool air into the engine, which causes overheating.
8 Use a screwdriver to adjust the idle mixture screws on your carburetor. Enrich the mixture by turning the screws outward until the engine begins to stumble. Turn the idle mixture screws inward slightly to obtain a richer mixture. A richer mixture will cool the engine temperature.
9 Inspect your cooling system. Replace the seawater pump impeller at the prescribed maintenance intervals. A hot engine will cause the fuel in the lines or carburetor to peculate or vaporize, causing vapor lock. If the water pump impeller blades have worn down, they can not push enough water through the system to adequately bring down the temperature.
10 Make sure all fuel lines and hoses do not mount or sit in proximity to the exhaust manifold of the engine. Heat from exhaust manifolds will boil the fuel and cause air pockets, starving the engine of liquid fuel. Reroute all hoses and lines a safe distance from the exhaust manifolds.
11 Avoid using WOT on very hot days, especially when pulling heavy gear, passenger loads or skiers. The combination of high outside temperature and constant high acceleration will overheat the engine and vaporize the fuel. Constantly monitor the engine temperature gauge for warning signs of overheating. Shut the engine down and let it cool for 2 or 3 hours before restarting after you have suffered a vapor lock condition.
12 Change the oil when you notice a higher than normal running engine temperature. Oil that has lost its viscosity will create friction with the major engine components and add additional heat to the engine.