Outboard dies when throttling up from idle

[SteveSails]

Had the same problem with my 3.5 Merc which I believe is that same engine as the Tohatsu. Cleaning the carb helped but wound up replacing the jets... problem solved.
My small Honda engines, an EU2000 generator and a small snowblower, don't have that problem, I have left gas in both for over a year and they both started after a couple of pulls. So what does Honda do that the others don't?

[a64pilot]

Originally Posted by SteveSails

Had the same problem with my 3.5 Merc which I believe is that same engine as the Tohatsu. Cleaning the carb helped but wound up replacing the jets... problem solved.
My small Honda engines, an EU2000 generator and a small snowblower, don't have that problem, I have left gas in both for over a year and they both started after a couple of pulls. So what does Honda do that the others don't?

I have a half dozen small engines, mostly Echo brand lawn and garden stuff, I've had them for years, always run twice the amount of Sta-bil recommended (if you read the label it says this doesn't hurt) and have never had to clean a carb, same thing for years on my motorcycle, even left it a couple of times for a year at a time doing Army stuff and never had to clean a carb.
Good question, because it's not an isolated issue.

[SkiprJohn]

Originally Posted by a64pilot

I have a half dozen small engines, mostly Echo brand lawn and garden stuff, I've had them for years, always run twice the amount of Sta-bil recommended (if you read the label it says this doesn't hurt) and have never had to clean a carb, same thing for years on my motorcycle, even left it a couple of times for a year at a time doing Army stuff and never had to clean a carb.
Good question, because it's not an isolated issue.

Just a question because I'm always willing to learn. Do you use ethanol gas?

kind regards,

[thomm225]

Originally Posted by SteveSails

Had the same problem with my 3.5 Merc which I believe is that same engine as the Tohatsu. Cleaning the carb helped but wound up replacing the jets... problem solved.
My small Honda engines, an EU2000 generator and a small snowblower, don't have that problem, I have left gas in both for over a year and they both started after a couple of pulls. So what does Honda do that the others don't?

My small 5 hp 4 stroke Mercury doesn't have that problem either. I've done both run the carb dry and just stop the engine normally without problems.

Due to the fuel selector on the side, it's quite easy to run the carb dry after use.

Maybe that's the reason. The small 3.5 engines don't have the selector I don't believe and you would have to run out the fuel tank or unhook the fuel hose from the carb to run it dry and lots of folks probably don't take the time to do that..

Or those 3.5 hp engines and below must have really small jets etc. You see complaints on here about those engines, and I believe the Honda 2.0 and 2.3 also.

[Rustic Charm]

I've got the 3.5 hp Mercury which so are wouldn't have more than three hours on it at the most. Given its still very much under warranty I can't touch anything in it myself. I've taken it back to the shop once and complained and they were very specific that I don't need to run it dry.

I'm going down today and intend on giving it a good run on the dingy but if it keeps stalling I'm going to be asking for a refund. And mine doesn't just stall when accelerating, it stalls, dies and then I can't get it going without a significant amount of trying.

[Bregts]

I have the mercury version of this engine which is the same. The tohatsu, nissan and merc 2.5 and 3.5 are the same engine. The more powerfull models 4 or 5 hp or not the same from these brands.

What can I say .... Read the reviews of this engine on the west marine website, you are not alone. I'm fulltime cruising with this engine for the dinghy and I have to remove and clean the carburator once every few months/weeks. When not using it, even for a few days make sure to run it dry using the fuel on/off on the starboard side, if the engine stops after shutting off the fuel shake it a bit and you can run for a few seconds again. Do this to make sure you get all fuel out of the carb.

The problem you describe sounds as a clogged carburator, get the fuel tank off, remove the 2 screws that hold the air intake and carb and take the carb off. Open it, clean it and spray wd40 true every opening you see. Screw the main (brass) jet out and make sure the tiny tiny hole is clean.

Assamble again an you are good for another few weeks

3 weeks ago I cleaned the carb, all fuel lines, the tank, changed the oil, sparkplug and tailoil and even then it stays a wild guess if we will get to shore or to the boat. 2 days ago we had to be towed to the boat again.

This is the most unreliable equipment we have on board.

[thomm225]

A bit off the thread but check out this service manual that is available online for the Mercury 4-5-6 hp outboards:

Boatinfo - Mercury Service Manual for 4-5-6 hp

[MarkSF]

Originally Posted by Cormorant

Good to know that Seafoam alone doesn't prevent things like this, if the gas is left in there.

Of course it doesn't. Does Seafoam prevent gasoline from evaporating?

[SkiprJohn]

Our club has a Mercury 6 and it is still going strong after a couple years. Maybe it's just the engine and not the fuel problem.

Our dealer won't honor the warrantee if we use ethanol fuel in it. That's why I asked the question.

[Scout 30]

Because ethanol absorbs moisture in the air it is also a good idea to keep the fuel tank full & the vent cap closed when you store the motor. I strongly recommend using non-ethanol fuel if possible.

[BlueCristal]

I use 95 or 98 octane as the quality of fuel is much better and less likely to gum up and the extra cost is minimal for the the numbers of litres used. I use the same for my cars, ride on mowers etc, its worth it in the end. Does anyone else agree with my experience?

[Rustic Charm]

Well, I have just got back from trying mine again. Brand new engine and I couldn't get it to tick over at all. So it's back to the shop on Monday. Either they fix it permanently or I'll be wanting a refund. Less than three hours use and I'm using the best fuel.

[MarkSF]

Originally Posted by Rustic Charm

I've got the 3.5 hp Mercury which so are wouldn't have more than three hours on it at the most. Given its still very much under warranty I can't touch anything in it myself. I've taken it back to the shop once and complained and they were very specific that I don't need to run it dry.

I'm going down today and intend on giving it a good run on the dingy but if it keeps stalling I'm going to be asking for a refund. And mine doesn't just stall when accelerating, it stalls, dies and then I can't get it going without a significant amount of trying.

They are wrong about not running it dry. All these small 4 strokes have very small jets, and good practice is essential.

By good practice I mean :

Run it dry
Use a stabiliser
Use only fresh fuel

I ran the same Tohatsu 3.5 for two years, without problems, doing the above.

You can blame ethanol, you can buy 100 octane gas. But the simple fact is that ALL gas evaporates to leave a residue, and people have been rebuilding carbs since the invention of the internal combustion engine.

[MarkSF]

Originally Posted by David M

This is typical of a clogged carburetor jet. When alcohol in the fuel is allowed to dry inside of the carb, a residue is left behind that can clog the jet. There are no additives that are effective that I have ever found. The best thing to do is to is to disconnect the fuel line and let the outboard burn the remaining amount of fuel out of the carb when you are done with the engine.

Alcohol leaves no residue when it evaporates. Gasoline does.

[SkiprJohn]

I will blame ethanol for leaving an orange gooey mess in my carburetor which was never there prior to ethanol gas. I had to rebuild the carb on a big Honda generator just because of the goo. Nasty stuff that does not disolve away with carb cleaner.