If the engine is optimized for it with higher compression and whacko ignition timing, ethanol can make more power than gasoline. When the class allows, a lot of top autocrossers use the stuff.

But your range will suffer mightily...

The action that saved you?.
 

"When I was sure that the landing was assured I forgot about the engine and focused on the landing, I slipped with full right pedal and slowed down in order to set flaps down again."

I have been reading all of the accidents in the RV data base. It is very sobering to see how many people have lost track of their airspeed and stalled on approach after managing the initial emergency. Great job flying the plane.

Sounds like a classic case of carburetor icing to me - low power setting (throttle plate closed down,) high humidity (visible vapor in the area,) relatively low OAT.

yes, and I should have said good job getting back in one piece. all the best to you and thanks for the post for this experience.

Uh oh, looks like it was not ice...
I uncowled and stared at the engine for a few minutes, everything looked fine.
No sign of blue stain typical of avgas on the carb neither below it.
I opened the andair gascolator and checked the filter, it was fine.
After closing the gascolator, I turned the facet auxiliary fuel pump on in order to check for leakage.
Few seconds later there was a big leakage coming from the filter air box.
I had this problem by the end of 2013, when I decided to overhaul the carb, a nice chance to comply with the bulletin regarding the replacement of the metal floats by the synthetic material floats.
I discovered this issue because of a fuel leakage that developed 10 to 15 minutes after a flight.
Few flights later it was leaking again.
The carb went back to the shop that checked it out and I never had fuel leakage again for more than 1 year.
In the morning, I started the engine, very strange behaviour, black smoke and vibration, I tried to shut it down closing the mixture but it did not work, I had to shut it down via ignition switch.
In the afternoon, I started the engine again, a little bit of the same strange behaviour but in less than one minute it was running as usual. I checked full power, mags, idle, everything ok. Shut down normally closing mixture. No leakage during the cool down.
It looks like an intermitent problem.
Fuel system is very simple, on more comment about it is that I have a primer solenoid with a fuel line that goes from the gascolator to all 4 cylinders intake.
Any clues?

I'd would second the carb ice. At speed, the total air temp in th carb would be higher. At reduced throttle the temp would drop.

Less than 10c and visible moisture... Suspect ice.

Flooding
 

Is it possible your flooding the engine with the facet fuel pump? Have you checked the max fuel pressure allowed on your carb? Your pump could be over pressurizing the carb, you might need a pressure regulator inline on facet.

Hi,

The fault is itermittent, what is causing me difficulties to make it happen again.
Any way, I can only reproduce the fuel leak or the engine rough operation when I command the primer solenoid to open.
So, I am convinced that it is the source of trouble.
Wow, I could never imagine that someday I would fall from the sky due to a so stupid failure.
Now I am thinking about what to do next, replace the solenoid or remove the primer system?
Regards,

Ramiro

simplicity helps keep our machines in the sky.

Supposing that the primer system was the culprit I replaced the parker solenoid valve, the switch and the circuit breaker.
Everything worked fine for the last ground tests and flight hours.
But, unfortunately the problem showed up again last weekend (april 26 2016) in 2 consecutive flights.
This time the engine did not quit completely.
It entered a kind of sub idle mode close to 450-500 rpm when the normal would be 800 rpm.
Reverting back to the carburetor...