Outboard dies when throttling up from idle

[DeepFrz]

Scroll down the 2nd page to see the deposits in a carb.
Tohatsu 3.5A Carb Page: 2 - iboats Boating Forums | 576722

[Nicholson58]

Originally Posted by bstowers

I have a less than 1 year old Tohatsu 3.5 hp 4 stroke that use for my dinghy. Most all of the hours on it so far are just break-in hours that were done according to the service manual and have only had a chance to actually use it on trips a few times. It's stored in my garage on a stand and I use Seafoam treatment in the fuel (1 oz / gallon).

Something that is giving me fits is that about 90% of the time throttling up out of idle will stall. It will run fine at idle, and it will run at higher than idle but I almost always have to start the engine at something like 20% above throttle to use it. Very rarely I can gun it up out of idle and get it to make the transition, but most of the time it just stalls. Going slowly out of idle will stall it 100% of the time. Once it's out of idle it runs perfectly (both in neutral and under load), and in full idle it will also run perfectly.

Any ideas?

New engine - take it in for service. It wounds like it is not getting enough fuel. Fuel filter, fuel pump water in the fuel. We now use only non-ethanol fuel and our outboard runs better. We also had a stalling problem that I finally found to be two loose nuts holding the carburetor on the engine - big air leak & poor fuel intake.

[Rustic Charm]

Originally Posted by MarkSF

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.

I took mine into the shop today, after failing to even get it to start on Saturday. The owner of the shop got it to start but he was quickly able to ascertain there is a fuel problem and he also recommended I run it dry. I told him his small engine mechanic said not to and his response was the same as yours, 'he's wrong'. He recommended using premium fuel and running the carb dry. But he's also going to pull it apart because there is something wrong as well. Given it's a new engine, less than two hours, probably less than an hour of running time he's suspecting there are some left overs from manafacture in the carb.

[BlueCristal]

I was looking to 'upgrade' my 5 year old (minimal usage as tender motor) Yamaha 3hp 2 stroke for a Mercury 3.5hp 4 stroke but after hearing all these war stories not sure that is a good idea. My Yamaha exhibits some of the same issues of stalling when accelerating but usually goes away once warmed up and some throttle management.

[Rustic Charm]

Originally Posted by BlueCristal

I was looking to 'upgrade' my 5 year old (minimal usage as tender motor) Yamaha 3hp 2 stroke for a Mercury 3.5hp 4 stroke but after hearing all these war stories not sure that is a good idea. My Yamaha exhibits some of the same issues of stalling when accelerating but usually goes away once warmed up and some throttle management.

I upgraded my Yamaha 2.5hp 4stroke to the 3.5 Mercury 4 stroke. So far I have regretted doing that. My Yammy was a little old but it started well and went well. My 3.5 seems to use a significant amount more fuel for not that much gain in power. But my worst concern is that I just can't get it going, yet alone keep it going.

[a64pilot]

Originally Posted by SkiprJohn

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



kind regards,

Yes as it's difficult to avoid


Sent from my iPad using Cruisers Sailing Forum

[Azul]

In the iBoats thread linked in #31 above, the motor didn't start even after the extensive deposits were cleaned out of the carburetor. In that case the fuel valve was also full of deposits, and the bladder inside the valve was damaged (possibly by ethanol in the fuel?)

[Scout 30]

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've had the same problem with my Honda 2hp. I eventually replaced the carburetor. I only run nonethanol gas, run the carburetor dry & keep the tank full with the vent closed when storing. I also use Stabil.

I had a 25hp Honda that was so bad I sold it & bought a 25hp Yamaha 2 stroke that I absolutely love. My buddy has a Honda 40 on his Cat & a Honda 50 on his Caribiana. He's has so many problems with them that he buys all 3 carburetors already assembled on a manifold to make replacement easier. He's also had a lot of problems with them making oil. Somehow gas gets bypassed into the oil. To be fair several other makes of 4 strokes have this same problem.

I think a lot of the problems we're all having are due to ethanol & it's mandated to increase to 20%. Everyone needs to contact their congressman & support The Renewable Fuel Standard Reform Act of 2015.

[thomm225]

No problems here with 10% ethanol. My engine is a 5 HP 4 Stroke Mercury but it does get used since it's the main auxiliary engine for the boat.

In Winter, I start it monthly if possible. (if the water is on at the boatyard)

I run it dry in Winter. In Summer, I don't. No problems to this point. I've had it 3 years. It was bought new and seems the more it's used the better it runs.

I didn't use stablizer the first summer but after reading about all the problems with outboards on CF, I started using stablizer.

[Rustic Charm]

Another update from me today. I chased up how the shop was going with mine. The first problem was that the fuel cap for the small outboards up the the 4hp has an EPA approved cap with air vent. Surprisingly above four HP and they come with a non EPA cap. Why he doesn't know but when you order the cap it comes in both EPA and non EPA options.

Anyway, my cap was not letting the air in and starving the carb of fuel. That's the first problem he found. So he put a non EPA cap from a 6hp and that fixed the fuel starvation problem.

But, it was still stalling when accelerating and he couldn't fix that and believes it's a carb fault (on a brand new engine). He emailed the manufacturers who told him to just replace the carby. So, I still can't check mine out until next weekend.

[a64pilot]

Usually a four stroke "making" oil is from extended low power running, like trolling. But it can be from a poor ring seal, best action to try to cure the making oil is to run one hard, thereby seating or wearing in the rings.
It's diluting the oil with gasoline of course, it's not making oil

[Rustic Charm]

Another update on my Merc 3.5

Picked it up finally after the carb was replaced with a new one. Took it down to my boat and on to the tender. 4 pulls to start it and off it went. I was determined to give it a good go this time. Motored across into the bay among moored boats. After just 10 minutes it just died. 16 pulls and off I went again. After another ten minutes I went to my yacht and tied up. I took 30 minutes putting my yacht on my mooring and then climbed into the dink to go back to the jetty. Pushed off and tried to start it and 'nothing'. After a number of attempts I started counting and finally got it going on number 22. Piece of crap!

I immediately put it in the car and back to the mechanic. I made it clear this time, that it needs to be finally rectified or I want my money back.

Keep in mind this is a new motor I picked up in June last year. To date it has less than an hour of use on it. Because I've rarely been able to get it to keep going. Absolute rubbish machine.

[Scout 30]

At this point I think you should bypass the retailer & contact Mercury. They need to replace it or give you your money back.