This is for the outboard guys. A real head-scratcher this was. I put my little Whaler (15 foot Sport w/48hp Evinrude) in the water this year and it ran great all the way to the slip. I go fishing the next day and when I get up on plane it conks out like it's starving for gas. I assume it is the water-separator/filter because It was on it's third season. I wanted to see how long it could go without changing so I figured that was it. Nope. No change. I swap fuel tanks and it seems better. Nope, happens again. So over the next two months I am changing all sorts of parts looking for the fuel issue. New fuel pump, rebuild both carbs, change fuel lines, nothing helps. Yet, it is an intermittent problem. Some days it ran great, others not so great, some days it was terrible. It would get up on plane, run a bit, then starve for fuel like the bowls ran dry. Yet it would recover fine and run perfectly around 2000-2500 rpm. I could go all day at 2000 rpm without a hiccup. But anything up around 5000 and she would conk. Electrical parts all checked out. I was about to pull it out and take it home when I decided to just spend an entire day changing and adjusting everything. Nothing worked. Then I sat there wondering what I had done that may have been defective. Then it hit me- I always start the season with new spark plugs. I did not suspect them because the first day they ran perfect. I pulled them out and they both looked perfect- burning clean. I scrounged around in my tool box and found two old plugs and put them in. BINGO!!!! End of problem. Later testing would show 150 ohms on one plug but infinite resistance on the other plug so it was broken internally. It was jumping a gap inside the insulator. That would not in itself cause the problem. Maybe a high speed miss, but not a total shutdown. Then I got it. This motor has the S.L.O.W system (Speed Limiting Overheat Warning). If a sensor in the head detects an overheat situation a chip in the Module slows the engine down to 2500 rpm to prevent engine damage. The factory manual warns against routing the engine harness anywhere near the spark plug wires or coils. Because RFI (Radio Frequency Interference) from the ignition can trigger the S.L.O.W. system. Normal spark RFI is contained in the head but a spark plug jumping an internal gap outside the head at high speed is producing gobs of RFI. That triggered the S.L.O.W. system and when I slowed down the system disengaged and the motor ran fine. But not all the time. That's what was driving me crazy. So now I have a new SOP- test every spark plug for resistance before installing. I hope this helps someone from going through what I did.
