Mercury Question

[Juan Grande]

My father-in-law has a pontoon with an early 2000s (2003 or 2004) Mercury 4 stroke EFI Big Foot outboard. The motor has worked fine up until this spring. We launched it and the motor kept killing. He can get it to start, but he has to open it full throttle to keep it from killing. He replaced the primer bulb (which had a crack in it), the fuel line, fuel filter and added fresh gas, but he's still having the same problem. Seems like a fuel related problem, but not sure what else to try. I told him I'd post on FM to see if anyone had any ideas before we trailer it and bring it in to have a pro look at it.

Thanks in advance for any suggestions.

John

[BoxMN]

The easy stuff... does he change the plugs each year? The interval for that is 100 hours, which is about what I put on mine each year, so worth changing each year.

Did he just add fresh gas to a bunch of old gas? Or totally fresh gas? If he just added some, did he add it to ethanol gas? Ethanol gas is horrible, unless you will burn it all up real quick. Use non-oxy, especially in the fall/late summer.

Did he put any Seafoam (or other) in the off season? I put just a tad in each of my gas fillups throughout the year, and had been doing this will all my motors and small engines, and whether might be overkill, I have had good luck for years and years. If he hasn't yet, this might be worth it to try.

Lastly, it might just be time for a tune up possibly, especially if it has not been consistently run. Though honestly I am not sure what a tune up actually is with newer motors other than changing the plugs.

Good luck!

[leechlake]

with my Yamaha I've had problems with what I believe is the low idle jet getting clogged. I'm no mechanic by any means so I may have the lingo wrong but that sounds like a similar problem that I've had.

If it's like my pontoon that gets dropped off on our lake every year, I don't have a trailer, it might be best if you could get connected with a marine mechanic that will come to your place in his off time and get the jets cleaned.

[Juan Grande]

Thanks guys!

I already told him to buy new plugs since I'm sure he hasn't changed them in a few years.

He has a trailer so if we have to pull it out and bring it some place we can. Thought we might try the easy stuff first. I will mention the low idle jet, sounds like that could be the problem.

[BoxMN]

Juan, the top three plugs are pretty easy to get at with just long extension (I used my very long one as it was just easier) and socket and ratchet. The bottom one is a bit tougher, but you can do it without taking anything apart. But it is PITA that is for sure, just in the way they designed the stuff around it. You should be able to do it from the water no problem, if not too cold

I used a universal and extension and I think that is all. I know I have a flex head ratchet but can't recall if I used that or not, but it might be helpful if you have one.

Remember to check gap, as I bet his are so worn down that you will be scratching your head at the difference you will see

I know my buddies Yammie seemed to eat plugs, but I don't think he changed them every year either, until he found he should, haha!

Good luck.

[CaptainMusky]

One thing to also check, does he have a fuel/water separator on his boat? If not, a bunch of water could have gotten in there and messed with the injectors.

He should get a fuel/water separator and replace that filter anually. You would be amazed at the gunk and water that it catches and that wreaks havoc on small engines.

I know guys who have destroyed injectors on their outboards and had to replace them. Not a cheap fix.

[Juan Grande]

BoxMN,

Yes, I replace the plugs on my 2005 Merc 4 stroke and that bottom one is a PITA. The top three are easy with a a ratchet and extender though, like you said.

Not sure if he has a fuel/water separator. Does that come stock because I'm sure he didn't upgrade anything.

Would Seafoam help clean those injectors if that was the issue or would he have to get it serviced?

[CaptainMusky]

The Fuel/Water separator MAY come stock. Its usually done at your dealer. The Dealer I bought my boat from they install them on every new boat they sell, no exceptions. Others, not so soure. A buddy of mine bought from a dealer that had shops all over the state at one time and they didnt put the fuel/water separator in and that caused the issues with his Yamaha.

If the injectors are messed up, it could be possible to clean them with a more high power injector cleaner from your auto parts store, they would be able to suggest a good one, but Techron is pretty decent.

Seafoam would be good to use in each tank, but it may have a tough time really cleaning out something if it were really plugged. I love the stuff, but if this is the problem, it might be a tall task for it.

Hopefully he has the fuel/water separator. If not he could have issues down the line. It looks like a giant oil filter.

[harvey lee]

When u change the plugs, would not hurt to put some thread lube on the threads of the plug. I know my bottom one had some carbon on it and it was a bear to remove. The thread lube should cure that issue.

Mine were in for 2.5 years and it went way to long, motor was running well but the bottom plug was a issue getting it out wothout hurting the threads in that hole in the block.

Could save you some money if a plug seized up in the cylinder.

If you had any amount of moisture in the fuel, that could also cause your issues.

[BoxMN]

Also, maybe the mods would move this to the Boats forum, as those folks there know much more about motors and fixing them than I ever hope to. They have helped me many times - on my Evinrude, as my Mercs never need help hehe!

My pontoon (South Bay with 60 bigfoot) came with a fuel water sep. filter on the pontoon itself, and my older 97 Merc 150efi has one built into the engine. Essential to have I think, will save from problems, and easy and relatively cheap to install if you don't have one.

[Juan Grande]

Thanks for all the feedback, I knew I could count on you guys

I called him and there is a fuel/water separator on his motor. Should I have him clean that or can he replace the filter?

[harvey lee]

I would replace it, very easy to do. If you have the screw on type, it comes off like a oil filter.

[BoxMN]

Yeah, replace it. But if you ever are in a pinch, just empty it out into clear jar (not in lake of course ) and then put it back on, you will see if there is water when you look at what is in the jar. If you know you have some water in fuel, but not much (i.e. not enough to drain the tank), just keep doing this (remove, drain, put back on, lather rinse repeat...) until you have it all out, and then put a new one on.

[CaptainMusky]

Yep, replace it. Then replace again in the fall before you put it away, like the last thing you do. That way any water that gets in there over the summer you get out before storage.

One tip is to fill the cup inside the new filter with fresh gas before putting it on. That way it will have some fuel in it and then be easier to prime up when it gets time to fire up your motor.

[Juan Grande]

New twist, he's at the lake right now and said there is a lot of water in the gas tank. [PoorWordUsage]?

[CaptainMusky]

He is probably going to have to siphon that all out somehow. Not a fun task, but that is really the only option at this point. Bummer.

If it were a car it would probably be no big deal to run it, but small engines like outboards do not handle that well.

[CaptainMusky]

Once he gets all that gas out, then fill completely with Non-Oxygenated gas. Put some seafoam in there as well.

Ethanol in fuel absorbs water and is likely what caused this issue. Eventually it "breaks apart" and then you have what he is experiencing. Not a fun deal.

[delcecchi]

If you would like the service manual chapter for that motor, post or pm me your email.

[Kyhl]

Del, can you see if the water fuel separator is a separate filter can type unit or if it is a bowl under the cowling?

On my '04 merc 115 4S the water fuel separator is a plastic bowl in the fuel line that you unscrew and dump out then screw back on. If he has this type then don't replace it, just dump it out and reassemble. No cost.

The trick to these is the o-ring tends to swell making it tough to remove and even tougher to replace. I find it easier to replace the $0.49 o-ring at the same time that you clean the bowl.

There also is a red float in the bowl that you can use to visually check for water in the bowl without removing it. Water will sink to the bottom of the bowl and the float will float on top of the water. If the float is off the bottom of the bowl then there is water in the bowl.

Also, the fuel filter sits inside this bowl. Might as well change that while it's apart.

Of course, this all assumes you have the same water separator as my '04 Merc.

[delcecchi]

It ain't me with the motor. Sorry. But typically the cartridge type filters are an add on. Was for my Suzuki. And a bunch of water and bad gas in the tank will make the motor not run well.

If there is a portable tank with the right hose on it, that would be worth trying with nice fresh gas. If the problem clears up,l then what is in the tank is the problem and has to go.

[Juan Grande]

He syphoned out all the bad gas and replaced it with new premium gas, but it still did't start. I think he said there appeared to be water in he oil which I'm guessing isn't good. We ended up putting it on the trailer and towed it home.

We're still not sure if he has a water/fuel separator or not. Maybe I will take a pic of both sides of the motor and post them. I assume the function of that is to keep water from running through the motor and considering he has water in the oil, I would guess he doesn't have one.

[CaptainMusky]

Yeah, that would definitely be bad if there were water in the oil.

I do not have that particular motor, but by the sounds of comments by others there may be a "built in" fuel water separator.

My comments were about an external one that would probably be mounted in a storage compartment in the rear of the boat. It would be connected to the fuel line before it goes up to the motor(s) and not attached directly to or in the motor itself. The filter is larger like a big oil filter, the ones described by others must be considerably smaller.

Best thing to do now is dump all the oil from the motor and put some fresh stuff in there.

[BoxMN]

Not sure, but I don't think that motor has a built in one, mine is external. It is my 150 that has a built in one.