Issues with 1996 Nitro 185sf

[98nitro185]

1996 Nitro 185sf (150hp mariner)

About a year ago I inherited this boat from a family member and overall he said it ran great for 18+ years. In the past two years the boat has been having a very strange issue that 3 different mechanics can't figure out. The boat will go out on the lake and run like a champ for 2 hours to sometimes a half day but after time it starts cutting out. Example, we will be cruising at 5k rpms and all of a sudden the boat will slowly decrease in speed but its not a steady decrease. It will jump from 5k rpms down to 4k rpms then right back up to 5k rpms then down to like 3.5k rpms then jumps back up to 4.5k until it slowly goes to a slow crawl (sorry if that's confusing). For the most part the motor never dies and also there is zero alarms.

Recently we figured out that shutting off the engine and starting it right back up resolves the problem temporarily but comes back in about 20 minutes. We have taken the boat to Basspro and a few other boat shops around Phoenix locally and nobody can figure it out. They do several tests on the motor and say its a very clean motor without any issues. No overheating or leaks. I believe it's something with the fuel system but the mechanics say that they tested it and it checks out fine. The previous owner has dropped about $2,000 in a fuel pump and some other fuel related things trying to figure it out.

The boat overall is in great condition and has been garaged and very well maintained so we don't want to give up on it quite yet and that's why I am hoping someone on here can point us in the right direction. I know there is probably a lot more detail that is needed but I wanted to just start with something. Thanks again for your help!

[Mike Cork]

There are so many things that can cause intermittent problems. Because shutting it off and restarting temporaryly fixes it, I'd suggest fuel too. Something about letting the system depressurize is letting a blockage settle out of the way. This could be several things. First and cheapest is the squeeze bulb. The check valve in it can cause these problem. It's cheap to just replace it. I've watched grown men cry because a fuel bulb was cause intermittent issue that couldn't be duplicated. Then there is the fuel line deteriorating internally. A peice could be broke off and acting like a flapper valve and limiting fuel flow. With ethanol fuel I've seen this several times, only way to fix it is to replace all the fuel tubing. Before that, I'm sure these mechanics checked the fuel filter but it's normally not expensive and replacing it eliminates it as a cause.

If those don't fix it an electrical issue could cause these issues. I've seen a power pack go bad when it wants to, then start working when it wants too. You have several power packs and it's expensive to replace them all. If your only dropping 1k in RPM then just one is an issue. I'd recommend getting one and replacing the first cylinder. If I still does it, put the old one back in the number one spot and put the new power pack in the number two spot. Repeat until it fixes it. If that doesn't, take power pack back for refund (they probably won't refund you because it's electrical - if you know one of these mechanics he might let you borrow one they know is good)

Finally, do you have dirt dobbers in your area? I've again watch grown men go insane chasing intermittent fuel problems because a bug blocked or partially blocked the fuel tank vent system. If your vent is blocked the fuel tank will build a vacuum and make it increasingly difficult for the fuel pump to retrieve fuel. Shut the system down for a minute and let the vent catch up and all is good until the vacuum builds again.

All these problems can be very difficult for a mechanic to find because they don't happen until the motor is running for a while or are so intermittent that by the time you get the boat to then, the trailering, has shaken things into working order for the time being.

[Donald Garner]

98nitro185

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