The Evinrude 48-HP engine could run all day at 2000 to 3000-RPM. At 5000-RPM it would run dry.
Some times it ran great all day.
The first thing I checked was the spark plugs; they were clean with no fouling.
I checked all the fuel lines for air leaks. Each 6-gallon tank line has an in-line filter, and both were clean.
I tested the primer bulbs to make sure they were pumping fuel. They easily filled the bowls with fuel.
I made sure the portable tank vents were open.
I changed the Racor fuel-water separator.
I even tried two different fuel pumps.
Nothing helped. Then totally by accident I noticed something wrong while squeezing the primer bulb. I saw the in-line filter element moving back and forth while I squeezed. I immediately took the filter apart and found that the element inside was loose. The knurled ring that held it in place had unscrewed and was allowing the element to move around. Worse, the ring was covering two of the fuel path holes in the fitting. Then when the element moved it covered the other two holes. That is what was blocking the fuel flow, but not all the time.
I tightened the ring and put the filter back together. The engine ran great again. I feel silly not finding this bad filter earlier, but the filter looked fine at first glance and flowed fuel properly for priming. But full-throttle demanded more fuel than it could flow.
Being intermittent I didn't catch on that it only happened with one fuel tank. The other ran fine. As usual- it often is the simplest thing causing big problems.
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