Baffled. Can't get her to run.

I have a Carolina Skiff 198 DLV with a Yamaha 115 4 stroke. Both are 2011. We were running the boat on the lake last weekend at full throttle. After 8 minutes at full throttle, the engine bogged down and just died. After an hour of attempts to cool down/restart, we gave up and were able to flag down a tow. I got home and began to troubleshoot.

My first thought was gas.
Tested the fuel.
Changed the fuel/water separator.
New fuel filter.
Primed the line.
Checked the fuel pump, it's fine.

She started for about 3 seconds and died after all that work.

I thought maybe electrical, but why would she start for 3 seconds if it was electrical? I'm just baffled.

Pull the cowling and pull the fuel line that attaches to the bottom of the fuel rail that feeds the 4 injectors. Have someone stand back there with a mason jar or something holding that fuel line inside the jar. Key the ignition to the run (not start position) several times and and see if you get a 2-3 second blast of fuel out of that fuel line with each turn of the key to the run position... That turns on the HP fuel pump to build pressure before starting. If you get those strong continuous 2-3 second shots of fuel, you're getting fuel to the rail. If you lack a fuel pressure gage, have someone hold their thumb over that line tight and key it again (wearing eye protection)... should be able to tell if it is building some good fuel pressure.


If you've been running ethanol-blended gas and it is old, high RPM and vibration has a way of breaking lose lots of gum in the system in the engine and clogging the VST filter and the little filters in the fuel injectors. You can youtube "DIY fuel injector cleaning"... Pull them, get a 12V power source to connect to them one by one.. You'll hear them "click" open when you attach the power to each one and while each is clicked open with power attached to it you can "back-blow" carb cleaner through them and blow out any gum/crap that may be clogging them.

With regard to running a 4-stoke at WOT, I just don't do it. These aren't the old 2-strokes that can run WOT all day long. Lots of moving parts in these 4-strokes are really humming at 6,000 RPM.

I agree with not running at WOT,but others will disagree. You don't drive your car at redline and that"s a 4 stroke. If thread #2 doesn't show results, Test for a open gap spark,lightning blue snap. Has engine been overheated lately, Heat will play havoc with the electronics under the hood.

Thanks guys, I tested the fuel rail and everything looked good. I pulled a spark plug to check for spark and the engine started right up. Ran it for 20 minutes and she purred like a kitten. I can only draw two conclusions.

1) Spark plug #2 boot was very loose. Not even sure it was on there. I'm not sure with all the electronics on these things if it will still start without 1 plug firing.
2) Bumping the engine without the #2 plug freed up water and let the engine burn fuel. The fuel/water separator had a pretty good amount of water in it. Fuel/water was rusty in color. I was pretty disappointed because it just had it's 200 hour maintenance done at the shop. If they actually did the maintenance, the separator only had 7 hours on it. I'm convinced they didnt' change it out.

I appreciate the advice on the throttle. I've also heard mixed reviews. My mechanic talked me into a new prop so I could get her running at 6000 RPMs without issue. I typically keep her at 5000 RPM. I had her at about 5000 RPM when she bogged out.

I may be looking for a new mechanic.

Flywatt... Another thing that can be problematic with the F115 (learned this the hard way as well like everything) is the location of the VST tank is deep in the engine. I'm not saying this caused your problem based on what you described but it somethin to keep in mind when running it in the future... Running long or running fast generates ALOT of heat in the engine under the cowling. If you come to a stop and then shut it down they can be very tough to start again (especially if you are runnign ethanol-blended fuel with ethanol having a lower vapor point than gasoline. You can get a vapor lock with fuel/ethanol vapors in the VST tank filling the intake and creating a super-rich vapor situation that makes the engine almost impossible to re-start normally. If this happens you can advance the throttle (not in gear) to 1/2 -3/4 open and try starting... that will usually work and clear the vapor lock but be ready to yank back on the throttle to idle as soon as it fires. To avoid the problem altogether, always allow the engine to idle for 4-5 minutes and cool down after an extended or high speed run before shutting it off. If you don't, as soon as you shut it off hot the water drains from the block and the wter that was absorbing the heat is gone and it really starts to build heat under the cowling vaporizing fuel in the VST tank. Don't learn the hard way... The Yamaha manual says to allow it to idle and cool down for several minutes before shutting off. I didn't pay any attention to those instructions until I learned the hard way.

deepsea21 said:

Flywatt... Another thing that can be problematic with the F115 (learned this the hard way as well like everything) is the location of the VST tank is deep in the engine. I'm not saying this caused your problem based on what you described but it somethin to keep in mind when running it in the future... Running long or running fast generates ALOT of heat in the engine under the cowling. If you come to a stop and then shut it down they can be very tough to start again (especially if you are runnign ethanol-blended fuel with ethanol having a lower vapor point than gasoline. You can get a vapor lock with fuel/ethanol vapors in the VST tank filling the intake and creating a super-rich vapor situation that makes the engine almost impossible to re-start normally. If this happens you can advance the throttle (not in gear) to 1/2 -3/4 open and try starting... that will usually work and clear the vapor lock but be ready to yank back on the throttle to idle as soon as it fires. To avoid the problem altogether, always allow the engine to idle for 4-5 minutes and cool down after an extended or high speed run before shutting it off. If you don't, as soon as you shut it off hot the water drains from the block and the wter that was absorbing the heat is gone and it really starts to build heat under the cowling vaporizing fuel in the VST tank. Don't learn the hard way... The Yamaha manual says to allow it to idle and cool down for several minutes before shutting off. I didn't pay any attention to those instructions until I learned the hard way.

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I really appreciate the advice. I will make sure she idles from now on. Just bought the boat a few weeks ago. This is my first four stroke. I'm learning a lot!

flywatt said:

I really appreciate the advice. I will make sure she idles from now on. Just bought the boat a few weeks ago. This is my first four stroke. I'm learning a lot!

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New boat and new to this F115? Lesson #2 I learned the hard way... If at all possible, DO NOT use ethanol-blended gas you buy at 99% of gas stations. Search online and locate the few stations close to you or a marina close to you that sells 100% gas. You pay more for it but after a few times of limping back to port and then wrenching my way into and out of my engine to clean the VST filter gummed up with that ethanol-blended gumming gas and pulling fuel injectors for cleaning I'll never run that ethanol crap it in my engine again.

If you keep running ethanol blended gas (regardless of what additives you add to it) you'll be back here posting about more problems and your problems will be a clogged VST filter on the bottom of the high pressure fuel pump located DEEP in the engine and clogged fuel injectors. 1st time I went after that clogged VST filter took me about 5-6 hours to get in and out and I have ALOT of tools.

Run 100% real gas if available and always add the Green color Marine Sta-bil with every fill-up at the recommended dose (not the red color as that is just a bunch of ethanol that was used we had ethanol-blended gas as ethanol bonds with water). If you have a spin-on Racor style fuel water seperator that will take care of water in fuel issues. If you don't, check the little filter in under the cowling in the back of the engine.. you'll see a red ring that sits on the bottom and will rise up if that filter collects any water.

Replace that little filter every 2-3 years whether it needs it or not. Replace your thermostat every 3 years whether it needs it or not. replace your water pump impeller every 3 years whether it needs it or not. These things are cheap and pretty easily done on you own... A trip to the Yamaha Mafia Outboard Service Center is costly and you may as well re-mortgage the house for a new outboard these days. Do the above, cruise at 4200-4600 RPM in the "sweet spot" range and these F115's and all 4-stokes will deliver 1000's of hours of service just as the commercial fisherman know who rack up 1000's of hours and baby and take care of their 4-strokes.