Yamaha F115 2006 Motor Starting Problem

I've had my boat and motor since it was new and have never had any trouble with it until this year. Let me begin with the problem as it has progressed.

Motor wouldnt start on the second trip of the year. It would crank but not fire. After trying to start it over the next 20 minutes, the motor fired. It ran flawlessly the rest of the day. Turning off and starting the motor numerous times.

This past Monday I embarked on a weeklong camping trip in Voyageurs National Park, this was the fourth time it's been run this year. The motor started and ran great on the first day. After being docked overnight, the motor wouldn't start the next morning. I allowed it to sit for a half hour or so again, and it started. I ran it all day, starting and stopping it numerous times. The next morning it again wouldn't start even after allowing it to sit. This time it required a shot of starting fluid into the air intake. I ran it the rest of the day starting and stopping numerous times. The same thing happened the next day, with starting fluid to the rescue. My luck ran out the last day, with nothing working to get it started. My trip came to an early finish, having to be towed out of the park.

As as a note, I only have run non-oxygenated fuel through the motor. I experienced no loss of power or a rough running motor. Only the motor cranking without firing. I am a novice boat mechanic. Any help would be appreciated to get me going again! There is lots of summer left.

If the motor wouldn't fire even for a short time even when you are spraying starting fluid in, it is likely to be either spark or possibly even water coming through a blow head gasket. Watch this video and start to isolate each system to confirm it is working. If you step through methodically you will find the problem: https://www.youtube.com/watch?v=rXNXzs5Ggjs In fact the outboard used in this video has blown head gasket so you'll see the symptoms of that.

Stuart

I've checked the compression and all 4 cylinders and there is good compression on them all. I have found an issue with the spark plugs. New ones will be here tomorrow. Could it just have been that?

It could well be. What problem did you discover with the plugs?

Stuart

When it doesn't start you need to find out exactly what's missing, fuel or sparks? First is to check if you have sparks and make sure you have sparks to all the spark plugs. if you do then it's fuel related. If it's fuel related then it could be an intermittent voltage issue going into the fuel pump. Most of the time if it's voltage related it's a lose connection at the key switch where it sends the voltage to control the EFI relay on the motor. I have this same issue with my Suzuki four stroke and I just fixed it. it turned out it was a loose connection at the power wire going to the EFI relay on the motor. The symptoms would be no sparks to all the plugs, no power to the fuel pump and no power to the buzzer. Good luck.