Engine RPM issues after "winter"

[leeatmg]

We have our 2009 SX230HO in a wet slip here in Arizona year round. We tend not to use the boat between October and April or so, and this year was no different.

Took her out yesterday for the first time since October, and while everything started and ran fine initially, after I got out of the marina (out of the no wake zone) the starboard engine RPMs would jump around a bit (+/- 800-1000 RPM) as if the engine was revving and then trying to die. After several minutes of this, it stopped, but the port engine began doing the same and continued for 5-10 minutes until I ended the trip back at the marina. It never did cut out, and it did not feel like cavitation. No warning lights of any kind.

The gas tank is half full, so I'm wondering if the gas, sitting for six months half full, is the issue. Any thoughts?

 

[Crob83]

Was the gas treated at all before it sat for that period?

 

[leeatmg]

Was the gas treated at all before it sat for that period?

No - I have never treated the gas in the past. I've also never used fuel with ethanol as far as I know, if that matters.

 

[Crob83]

No - I have never treated the gas in the past. I've also never used fuel with ethanol as far as I know, if that matters.

I would fill her up with some fresh gas the rest of the way and a little stabilizer before you add more fuel and try again. Just my opinion

 

[Seadeals]

If you don’t top off the tanks before you let it sit, the air in the tank can easily develop condensation with each temp swing that then drips cumulatively into the fuel and sinks to the bottom and collects there. Additionally if you use fuel with ethanol, it can go through phase separation and cause similar issues. I suggest adding a stabilizer and toping off (preferably ethanol free) before you let it sit a while next time.

 

[2kwik4u]

'09's are still the MR-1's right? If so, aren't they really sensitive to spark plugs condition. I have no personal experience with them, but it's a cheap thing to do as a check.

 

[212s]

I would fill her up with some fresh gas the rest of the way and a little stabilizer before you add more fuel and try again. Just my opinion

I agree with this - after a few months the fuel will get stale if not treated and the engines will run rough. When storing or not using for more than a couple months, you should always fill up adding stabilizer and run the engines for a few minutes to get the stabilized fuel into the injector lines. The fuel will be good for 12 months or more and no issues.

 

[Seadeals]

'09's are still the MR-1's right? If so, aren't they really sensitive to spark plugs condition.

Good point @2kwik4u they are MR1s and can be sensitive to plugs if ignored. In this case since the issue was on one engine and then shortly thereafter progressed to the other, fuel is the culprit as a plug issue is unlikely to happen at the same time on both engines.

 

[InmyElement]

Definitely fuel..treat treat treat..with stabilizer. I treat through the regular season.

 

[leeatmg]

Thanks, all. That was my suspicion, but I fell victim to the "I've always done it this way and it's never been an issue" thing and just never bothered. That, and the very low humidity in Arizona, made me think it wouldn't happen to me.

I'll top off the tank, add stabilizer, and hopefully that's it. Having someone change the oil, so I'll have them look at the spark plugs too just in case since it is the MR-1 engines. No harm, and may just have him change them out anyway.

Really appreciate the responses @Crob83 , @Seadeals , @2kwik4u , @212s , and @InmyElement . Thanks!

 

[LakesideLaw]

New plugs should be installed every year no matter what. They are cheap.

 

[leeatmg]

Just a quick update here. I was able to get back up to the boat on Saturday, added Sta-Bil 360 to the half-full tank, let it run a few minutes in the slip, then took her out for a drive. Flawless performance. So either that was the issue, and the Sta-Bil did the trick, or some marine miracle has occurred. Either way, thanks to all who commented!

 

[FSH 210 Sport]

Sounds like the gas went bad and adding some fresh helped the situation.

Id run a treatment of Techron through a full fuel load. Add the correct amount of Techron to treat the entire tank and go for a long enough cruise that you run through 80% or more of that tank of fuel. When you get back, put in enough stabil to treat however many gallons you will need to refill the tank, and refill the tank with fuel. This is a very enjoyable way to get rid of that old fuel that was in the tank.

Since you are not running ethanol laced fuel all that you should need is the stabil.

Probably the best thing you can do is take your boat and drive it regularly....I know it’s a tough job, but I’m sure you can handle it!

Super glad it is all better now!

 

[leeatmg]

Sounds like the gas went bad and adding some fresh helped the situation.

Id run a treatment of Techron through a full fuel load. Add the correct amount of Techron to treat the entire tank and go for a long enough cruise that you run through 80% or more of that tank of fuel. When you get back, put in enough stabil to treat however many gallons you will need to refill the tank, and refill the tank with fuel. This is a very enjoyable way to get rid of that old fuel that was in the tank.

Since you are not running ethanol laced fuel all that you should need is the stabil.

Probably the best thing you can do is take your boat and drive it regularly....I know it’s a tough job, but I’m sure you can handle it!

Super glad it is all better now!

Thanks! Burning through 80% of a tank in one day will be tough, as the "large" lake we are on here in AZ is only about 7500 acres. Lots of laps. But I might be up to the challenge.

 

[212s]

Once the fuel is treated and if the boat runs ok with the mix, there's no need to burn through it rapidly. Just use it up over the next few weekends and fill up with fresh fuel again. Make sure when you leave it for long periods you add stabilizer and top up the tank, then run the engines for 5 minutes to make sure the treated fuel gets into the fuel lines and injectors so it will fire right up next time.