Bad fuel?

[Merlion]

Guys, I had my boat in storage at the marina for over 3 months due to the covid situation. My tank was left almost full (about 80%). After running the boat for the first time, I noticed a significant top end decrease (from 50mph to about 38mph).
questions:
Is this related to the fuel going bad? If so, Can this cause long term engine damage? (Or should it go back to normal once it cycles to newer fuel?
Are there any products I can use to help the engine clean the old fuel?
Tks!!

 

[KevJul2019]

Did you have any fuel additive in your boat???

 

[Merlion]

Did you have any fuel additive in your boat???

Not really, I’m a bit new to boating. When do I need to put some? What kind? Would the this cause damage to the engine?

 

[OrangeTJ]

It'll be fine, I'd wager. Might not even be "bad gas" - that speed loss could also signal that you need to put in fresh sparkplugs.

 

[Gym]

@Merlion you indicated how long your boat was sitting idle but not how old the fuel was. Bad gas will usually only result in bad performance unless contaminated with particulates that clog filters and injectors.

When was your last spark plug change? To treat fresh fuel you may want to use Marine Stabil 360 at each fueling and especially before storage. I also use Ring Free to prevent carbon deposits on the valves. Both are readily available at any marine store or online.

 

[Liveto99]

This will work great.

 

[feziwig]

I’ve always had the best luck with Startron Enzyme fuel treatment. Great thing is it can somewhat restore fuel that’s already gone bad. It’s not as effective as adding it initially but helps. I’d add that and then top off with super. And yes spark plugs too, especially if it’s been a while. I notice most members here change annually regardless of hours which is great maintenance too. Especially since these motors ( especially the MR1, not as bad with the 1800 that you have) are very secceptival to corroded and seized plugs. Aside from poor running and speed losses, corroded plugs can be a major nightmare so good preventative maintenance

 

[WREKS]

I have used ethanol free gas early on. I know it is more expensive. When it is laid up, I run the motors every couple of weeks for a few minutes. Not so easy for some.

 

[tdonoughue]

Before going to extreme measures (and I don't mean Stabil 360--I use that on every fillup), be sure to try again. These boats can be surprisingly affected by wind, current and load. If you were going into a headwind, I would not at all be surprised at a 10mph drop. Also, if there is chop. Or a few extra folks on board. Etc. You may actually have no problem other than changing conditions.

 

[Babin Farms]

Storage??? If left in the water for 3 months it could be growth on the hull that would be a decrease in speed

 

[Merlion]

Storage??? If left in the water for 3 months it could be growth on the hull that would be a decrease in speed

Good point, however the boat was on a dryrack above ground. It’s definitely engine related

 

[Merlion]

@Merlion you indicated how long your boat was sitting idle but not how old the fuel was. Bad gas will usually only result in bad performance unless contaminated with particulates that clog filters and injectors.

When was your last spark plug change? To treat fresh fuel you may want to use Marine Stabil 360 at each fueling and especially before storage. I also use Ring Free to prevent carbon deposits on the valves. Both are readily available at any marine store or online.

Thanks this is helpful. The fuel had been put on the boat shortly before last trip, so it was about 3 months old.
I changed sparkplugs recently, (about 7 months / 25 engine hrs)
Quiestion: do you use both Stabil 360 and Ring Free at the same time? (How often should I use these two?)

 

[Gym]

Thanks this is helpful. The fuel had been put on the boat shortly before last trip, so it was about 3 months old.
I changed sparkplugs recently, (about 7 months / 25 engine hrs)
Quiestion: do you use both Stabil 360 and Ring Free at the same time? (How often should I use these two?)

I use these additives at each fill per bottle directions.

 

[jsg73]

Startron more better in my opinion. It goes in every time I add fuel to any boat.

 

[Liveto99]

If I’m going to use most of the fuel I don’t add anything when my boats going to sit for a while a.k.a. more than three weeks I throw stable in it. I always use alcohol free gas in the boat though.

 

[JeffCox]

I use Startron every fuel up, unless I know I will burn most of it that day. Had a mechanic tell me he has never had to take apart an engine he knew was regularly using Startron. Also use it in small yard too engines and jet skis. Never had a problem since I started using it. Could b overkill, but I Use it even in supposed ethanol free gas.

i have also used Seafoam in engines I thought were running rough because of bad gas. Many times, that will solve the problem.

 

[RobbieO]

I treated my full tank of gas in September and the boat hasn’t been on the water yet. Went to the Lake last weekend, but wasn’t able to launch. I fell off the bow and hit the pavement and messed up my foot pretty good. Luckily I didn’t hit the tongue of the trailer. You think my gas is still good?

 

[FSH 210 Sport]

I treated my full tank of gas in September and the boat hasn’t been on the water yet. Went to the Lake last weekend, but wasn’t able to launch. I fell off the bow and hit the pavement and messed up my foot pretty good. Luckily I didn’t hit the tongue of the trailer. You think my gas is still good?

Man, sorry to hear about your accident… hope you heal up quickly!

Yes, your gas will be fine. Most fuel treatments will keep the fuel good for two years… what treatment did you put in?

 

[RobbieO]

Man, sorry to hear about your accident… hope you heal up quickly!

Yes, your gas will be fine. Most fuel treatments will keep the fuel good for two years… what treatment did you put in?

Fuel Med Rx…Thanks…I put 48 oz in

 

[FSH 210 Sport]

Looks like you’re good!