Why are outboards so unreliable?

[Cliffhanger]

I have lost count of the outboards I have owed over the years but they all had one thing in common, they were all totally unreliable pieces of s#!t. This weekend for example I anchored near a nice beach so took the dinghy with my near-new Mercury 6hp 4 stroke outboard. Was running fine then suddenly died...anyway, long story short I ended up spending half the day unsuccessfully trying to get the damn thing working properly. It would run for a while and then splutter or just stop. I did all the usual things, drained the carby, drained the tank. Replaced the fuel with fresh. As I left the anchorage there was another guy drifting in his dinghy trying to start the damn thing, so at least it isn't just me.

If cars were this unreliable, nobody would drive them.

[goboatingnow]

All small four strokes can be notoriously poor at starting , the primary problem is the jet orifices are very small and the ethanol in gasoline gums them up as most outboards don’t get enough use.

I now dose all my fuel with fuel / carb cleaner and fuel stabiliser usually about twice dosage reccomendated, my mariner 3.3 4 stroke runs much better as a result , fresh fuel on its own won’t cure the problem.

My 15 hp two stroke Yamaha is abused forgotten about , dragged out of the shed , old fuel , starts first pull everytime !!!

[skipmac]

Agree that 90% of the problem is the fuel, both due to ethanol added and also gasoline these days isn't the same blend and quality that it was in the past.

It's not just outboards. I have problems with every small engine I own. The secret is to always drain all the fuel out of the engine if it's going to sit for a while. How long is a while is a good question. I figure more than a few weeks. Not only should you run it dry but depending on the engine you might also need to drain the float bowl of the carb. Since I've been doing that regularly my small engine problems have pretty much ended.

I also have a 15 HP, 2-stroke Yamaha that I would not sell for love nor money. Well maybe for enough money but it would take a lot.

[GordMay]

Originally Posted by skipmac

Agree that 90% of the problem is the fuel, both due to ethanol added and also gasoline these days isn't the same blend and quality that it was in the past...

Ethanol* aside, it makes no sense, to me, that producers have spent decades of effort, and expense, refining [pun intended] their product, to produce an inferior blend.
* IMO: The abomination of E-fuels was the creation of greenwashing marketers, and corn producers.

[thomm225]

I have basically the same engine 2011 Mercury 5 Hp 4 stroke 25" shaft bought new, and I have Never had a problem with it.

The main difference between from yours is the shaft length and that it has an integral 40 ounce tank if you are just going short distances you don't need the external hose hooked up which for me is often such as for just getting out of the marina

It's the main auxiliary for my 6600 lb displacement Bristol 27.

Do you treat the fuel with something like Sta-Bil because if it stays in the tank too long without being treated it will absorb moisture? If not, you need to. I use my fuel from October/November until the following Spring starting the engine at least once every two weeks all Winter.

Also the bad fuel can foul the carburetor.

So what I have down is add a few ounces of Sta-Bil to any fuel I believe will be in the tank more than a month which is most of the time.

Also I try to run the engine at least once per week. I even started mine a couple days ago when is was about 33 degrees out.

My engine is over 10 years old and has been a pretty great engine but I have owned like 6-7 other outboards over the years which probably helps.

These new 4 stokes though are so much better than the 2 stokes I used to have plus they are very efficient.

I can motor across the entire 20 miles of the low bay on a little over a gallon of gas.

https://www.youtube.com/watch?v=uNl2tPRC-Tw

https://www.youtube.com/watch?v=cpZhq35etcw

[thomm225]

Originally Posted by skipmac

Agree that 90% of the problem is the fuel, both due to ethanol added and also gasoline these days isn't the same blend and quality that it was in the past.

It's not just outboards. I have problems with every small engine I own. The secret is to always drain all the fuel out of the engine if it's going to sit for a while. How long is a while is a good question. I figure more than a few weeks. Not only should you run it dry but depending on the engine you might also need to drain the float bowl of the carb. Since I've been doing that regularly my small engine problems have pretty much ended.

I also have a 15 HP, 2-stroke Yamaha that I would not sell for love nor money. Well maybe for enough money but it would take a lot.

Actually you don't need to drain the fuel you can just use a treatment product like Sta-Bil.

I use the fuel I buy in late Fall all Winter and most of the following Spring because I treat THAT fuel as soon as I buy it with a few ounces of Sta-Bil.

I have done this for the past 9 years or so with my engine which is the same as the OP's

[thomm225]

Originally Posted by skipmac

Agree that 90% of the problem is the fuel, both due to ethanol added and also gasoline these days isn't the same blend and quality that it was in the past.

It's not just outboards. I have problems with every small engine I own. The secret is to always drain all the fuel out of the engine if it's going to sit for a while. How long is a while is a good question. I figure more than a few weeks. Not only should you run it dry but depending on the engine you might also need to drain the float bowl of the carb. Since I've been doing that regularly my small engine problems have pretty much ended.

I also have a 15 HP, 2-stroke Yamaha that I would not sell for love nor money. Well maybe for enough money but it would take a lot.

This is true and is the reason you cannot use it the same way as we did in the 70's and 80's.

Put in a few ounces of gas treatment like Sta-Bil in your fuel if you think you will have it more than a month and your engines will be fine.

If you notice those that use small engines all the time always seem to have them running fine.

I'll be running mine today. Temps have been in the mid 20's so I haven't started it in a few days ....which will give it a good salt water flush also

As far as other maintenance in 10 years, I have replaced the plug once, fuel filter once, and impeller maybe 4-5X plus greased it a couple times and changed the 15 ounces of oil yearly. I have also flushed it with fresh water 5-6 times in 10 years.

[Chotu]

It’s because you have a carburetor. Get a fuel injected outboard and you’ll never have these problems again.

Mine all start and run like a Toyota car now.

[Oldwheels]

Put an inlinefuel filter on it. Available from the lawn mower shop. Keeps crap out.
All small mercury engines are made by Tohatsu. Same engine, cheaper parts.
One thing I found on mine was this mount the coil, clean the mating surfaces and reassemble. But mine is 10 years old.

[Tetepare]

Outboards need maintenance like everything else. Plugs, wires, carb. Keep in mind that outboards are run high speed and WOT a lot more than cars.

My outboards have been reliable when maintained. The only reason I got rid of the 1964 Johnson was because I needed a 15. The 2 stroke Merc is now about 20 YO and runs great.

[thomm225]

Originally Posted by Chotu

It’s because you have a carburetor. Get a fuel injected outboard and you’ll never have these problems again.

Mine all start and run like a Toyota car now.

The smaller outboards like the OP's 6 hp only have carburetors.

[thomm225]

Originally Posted by Oldwheels

Put an inlinefuel filter on it. Available from the lawn mower shop. Keeps crap out.
All small mercury engines are made by Tohatsu. Same engine, cheaper parts.
One thing I found on mine was this mount the coil, clean the mating surfaces and reassemble. But mine is 10 years old.

The OP's engine already has an inline fuel filter. Maintenance schedule says to replace every year but I have only replaced mine once in 10 years.

It's all about treating the fuel ......

[thomm225]

Originally Posted by Tetepare

Outboards need maintenance like everything else. Plugs, wires, carb. Keep in mind that outboards are run high speed and WOT a lot more than cars.

My outboards have been reliable when maintained. The only reason I got rid of the 1964 Johnson was because I needed a 15. The 2 stroke Merc is now about 20 YO and runs great.

Maintenance.

The new 4 stokes don't require quite as much as the old 2 strokes. I have replaced the plug once on my Mercury 5 hp 4 stroke.

Fuel filter once. Fresh water flushed 5-6 times in 10 years. Impeller replaced 5-6 times. Replaced the 15 ounces of oil yearly.

No wire replacements. No carb cleaning, but I do treat the 10% ethanol fuel I use.

[thinwater]

Originally Posted by Cliffhanger

I have lost count of the outboards I have owed over the years but they all had one thing in common, they were all totally unreliable pieces of s#!t. This weekend for example I anchored near a nice beach so took the dinghy with my near-new Mercury 6hp 4 stroke outboard. Was running fine then suddenly died...anyway, long story short I ended up spending half the day unsuccessfully trying to get the damn thing working properly. It would run for a while and then splutter or just stop. I did all the usual things, drained the carby, drained the tank. Replaced the fuel with fresh. As I left the anchorage there was another guy drifting in his dinghy trying to start the damn thing, so at least it isn't just me.

If cars were this unreliable, nobody would drive them.

Poor fuel management. Cars burn more and have much larger carb jets (well, they don't have carbs anymore, but larger clearances). Cars also have sealed fuel tanks that breath only through carbon filters (no moisture). The problem is nearly always a bit of aluminum corrosion product either in a jet or under the float seat. Ethanol has made the corrosion problem worse, but ONLY if you allow moisture to absorb into the fuel. Unsurprisingly, brass jets in an aluminum body make a great corrosion cell.

• Keep the vent closed at all times when not actually running. E10 attracts moisture, and volitiles (which help it light) evaporate.
• Use an anti-corrosion additive, such as Biobor EB, Merc store-n-start, or Stabil 360. Most are snake oil.
• Run the motor at least monthly, if at all possible. Cars that don't run for months are not always reliable either. Run it enough that the gas never exceds 6 months old. You change the oil, same idea.

Draining the tank and changing fuel would not be expected to make a difference. Only mechanically cleaning out the jets (a very small wire).


I have not had a motor take more than a few pulls to start in 25 years, since I began these practices. But I have worked on plenty of OP motors.


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Yes, e10 is a politically motivated curse, but you can also easily learn to live with it.

[MicHughV]

My favorite engine of all time was a 8 hp Yamaha 2-stroke. Light weight, can pick it up with one hand, and ran like a swiss watch, never once, not the slightest hiccup.
I've had a succession of other 2-stroke engines, 15 hp.....Suzuki, Yamaha, all ran like a swiss watch. Now 4 stroke engines, Yamaha.

I don't know much about Mercury engines, but it seems like they have an unusually high complaint issues.