Démarrer un moteur. Particulièrement pertinent l'hivr
Priming Reprinted from Lycoming (with comments by Joe Rathert)
Probably the most important factor in starting an engine is achieving a fuel/air mixture that is satisfactory for combustion. (note that this is a fuel/air mixture! liquid fuel is not doing you any good JR) Since the engine usually starts very easily, many pilots are unaware of or ignore the change of starting procedure needed to successfully start under varying temperature conditions. In warm weather, the air is less dense, and therefore must be mixed with a lesser amount of fuel than in cold weather. In addition to this, in warm weather, the fuel will vaporize readily and make starting easier. Simply stated, as temperatures go down it becomes more and more important that we have a plan for priming that will achieve the correct fuel/air mixture.
When priming a carbureted engine, the pilot’s plan must consider the temperature, the number of cylinders which have priming lines installed, and the number of strokes of the primer needed to produce the correct fuel/air mixture. The primer lines are ordered or installed by the airframe manufacturer and not all aircraft are configured the same. Some aircraft have actually been produced with only one cylinder being primed, and these engines are extremely hard to start in cold weather. The number of cylinders that are primed must be considered since the total fuel delivered by the primer will be divided and sent to these cylinders. As the air becomes colder and denser, the amount of prime used must be increased, but the number of strokes to be used should be planned as a result of some trial and error experimentation for each aircraft a pilot flies. When the correct number of primer strokes for each temperature range has been established, the engine will usually start very quickly. We may find that an engine starts easily when one stroke of the primer is used in the 60˚ range, two strokes in the 50˚ range, three strokes in the 40˚ range, etc. This is an example of the trial and error we might use to establish the number of primer strokes to use under any particular temperature condition.
The amount of fuel must be varied with the temperature but it also needs time to vaporize. When its warm 30 to 45 seconds is enough time, when it’s cold wait up to one minute. I prime and then go through the prestart checklist. Using this method the engine starts cleaner (more like a car) and I use less prime (2 strokes unless very cold). Because you want the fuel to vaporize push the primer in quickly and firmly. This helps atomize the fuel as it is injected into the cylinder. Conversely, pull the primer out slowly and give it time to fill before pushing it in. If it goes in easily for a portion of the travel it wasn’t full. JR
Do NOT pump the throttle to prime. JR
The Prime injects fuel into the cylinders (generally 3 of them). Lycoming engines larger than 118HP have an accelerator pump in the carburetor. This pushes fuel through the venture. See the figure. Since the carburetor is mounted on the bottom of the engine and is an updraft carburetor any fuel pumped through the venturi, without the engine cranking or running, will fall (that gravity thing you know) into the airbox. A backfire on start will ignite this fuel and you will have the opportunity to practice that fire on start bold face procedure you memorize every year for your Form 5. You can over prime using the primer but it takes a lot of fuel to get back into the induction system, run down the induction tube into the carb and drip into the airbox. JR
If, after you have primed using the primer, you feel compelled to pump the throttle (and we all have) only do it 1 or 2 times max, and the engine MUST be cranking. If it still does not start, STOP and WAIT JR
While discussing the priming of an engine, there have been situations where primer lines have become clogged. This makes engine starting difficult and negates any trial and error experimentation that may have been done. When maintenance is done on an aircraft before the start of winter, it may be wise to have those primer lines checked to ensure that fuel will flow through them.
The amount of fuel needed to achieve the correct fuel/air mixture for starting a fuel-injected engine is controlled by timing rather than number of primer strokes. With the electric fuel pump on, moving the mixture control to the rich position allows fuel to flow to the cylinders. For cold-weather starting, it may be necessary to keep the mixture control in rich somewhat longer than in warm weather.
The fuel part of the fuel/air mixture may be the part we have the most control over during the engine start, but keep in mind that the amount of throttle opening does have an effect on the air that is pumped through the engine. Just as we compensate for cold/dense air by adding more fuel for start, it may also be appropriate to reduce the air part of the mixture when the temperature is very cold. For example, if the throttle is normally set open one-half inch for warm weather starting, it may be helpful to reduce this to one-quarter inch in cold weather. Again, it will require some experimentation to determine what is needed to achieve the correct fuel/air mixture for any particular aircraft at any temperature range.
When an engine does not start easily, it can be frustrating. Of course, this can occur at any time of the year, and it is very tempting to just keep grinding away with the starter in an attempt to get it going. Should this happen to you, RELAX. Take care of that starter, or it may fail. The general rule for starters is that they should only be operated for short periods, and then allowed to cool. If engine start has not occurred after three 10-second periods of operation with a pause between each, a five-minute cooling off period is required. Without this time limit for operation and an adequate cooling off period, the starter will overheat and is likely to be damaged or to fail completely.
Guess what! This also gives fuel an opportunity to vaporize and blow away. If you prime more than 6 strokes (counting the use of the primer and the two you probably did with the throttle) and it has not started wait at least 5 minutes before you try again. DON’T KEEP PRIMING. You already have too much fuel and not enough air TAKE A BREAK. JR
The previous paragraphs have addressed several issues that relate to the cold-weather preflight and the cold-weather start. There are other cold-weather items that should be considered in the operation of the engine.
Assuming the engine has kicked off, check for an indication of oil pressure. Learn the characteristics relative to response of oil pressure indications of your aircraft/engine combination. On most single-engine aircraft, an almost immediate response is noted. On twin-engine aircraft, the response may be much slower. On some twins, the oil pressure may go up, and during warm-up, may drop again for a short period of time, then again rise to normal. All cases mentioned may be normal, but the important thing is to know what to expect from your aircraft/engine combination.
Note where the fuel enters from the venturi. Without air being sucked into the engine fuel will fall and puddle in the airbox. JR
From the American Flying Academy
• The American Flying Academy
There are typically two “schools of thought” as to what a CFI teaches their students regarding the proper way to start the engine. Generally the CFI teaches what they learned from their CFI when they were students and the CFI’s CFI learned from their CFIs and so on perpetuating the cycle of information.
There is a common trend of teaching the improper procedure for starting engines and it happens because at the end of the day, the engine started, so that must have been the proper method.
Typically the Instructor will show the primary student that they should give the throttle about three “pumps” and then hold the throttle ¼ inch open before cranking the engine. And behold, the engine starts, and they’re off to fly.
What’s wrong with this practice? It works doesn't it?
Well, the configuration of the engine induction system is such that the fuel comes from the bottom of the engine to the top into intake valves of the cylinder. The fuel discharge nozzle is positioned above the carburetor box. What this means is that when you give it those three pumps you are effectively spilling fuel over to collect at the bottom of the intake box away from the venturi, and permeating the air filter with fuel. This is the opposite of what you want to happen.
What you want to happen is for the fuel to be discharged and be immediately drawn up through the venturi where it becomes atomized into a combustible mixture that will then go into the cylinders to run the engine. This will not happen unless the engine is turning. When the engine turns, the actions created by the engine pistons and the intake/exhaust valves draw air up through the throttle body of the carburetor and this initiates the atomization process.
“But if I don’t ‘pump it’ the engine will take forever to start!”.
That will not be the case if you properly use the engine primer before you crank the engine (as stated on the Pilot Operating Handbook). What the primer does is to simply bypass the whole airbox, carburetor, venturi business and draws fuel from the fuel supply and injects it directly into the cylinder. If you don’t over-prime it, by pumping the primer 5-6 times (2 times is plenty), the engine will start right up.
What’s the big deal whether you pump the throttle or prime it, as long as the engine starts?
The big deal is that fuel tends to blow up/explode when exposed to heat. If the fuel explodes inside the cylinder, it will not do any damage. The cylinder is designed to contain explosions. The piston inside the cylinder will be pushed by the expanding gases and the engine will turn.
However, if the fuel explodes inside the air box, then you have a bit of a problem. Those air boxes are made of thin aluminum and have fabric hoses attached to them. They are not designed to handle fire. The aluminum will not contain the explosion and the fabric will burn. At the very least, you’ll have a fire to deal with, and at the worst, you’ll have a nasty explosion that may kill you.
This is particularly a hazard if you are in hot weather like South Florida, or in the desert. However it may also happen in the cold as well. If you are flying and land to refuel the aircraft, that engine is hot enough to ignite any fuel that is deposited into the air box when you go to restart the engine.
So those who have a habit of using the “throttle pumping” method should seriously rethink it. Just because it has worked all along without incident doesn’t mean that an incident can’t happen to you. All it takes is one time, and then you can have a really bad day.
des souvenirs 
Belle photo, c'était à quel endroit?
C'est là, entre autres, que t'as pas envie que ça niaise, pis faire des politesses au throtle control. 
j'ai extrapolé l'endroit sur mon GPS, mais si il y a plus précis je prendrai bien.