A beginner's guide to Engine Starting

What does the engine really want: The engine wants a mixture that is just very slightly rich of stoichiometric.  That is, a fuel-air mixture that will ignite the best. When that happens, the engine will start quite easily.  The engine in your car, although you have the advantage of modern electonics measuring the outside air temperature and the engine temperature and having a computer to adjust everything, needs the same thing.

By-the-book, i.e., POH:   Back in the olden days, the engineers at Lycoming assumed pilots were basically stupid.  They expected pilots didn't have a clue as to how an engine worked.  The engineers were not entirely wrong for the most part. 

Engineers decided that, if they told the pilots to start with an overly rich condition and then used a method to gradually lean the mixture then most engines would start right away. To do this, the POH instructs the pilot to prime the engine, 3 squirts, 4 squirts, however many, crack the throttle by 1/4 inch and then start the engine.  Cracking the throttle allows air into the cylinders to lean out the overly rich mixture.

But, what if the mixture is not rich enough and it won't start?  What if the mixture is too rich and when the engine doesn't start right away the pilot primes some more?  Under ideal conditions, you've done everything you need to do and the spirits all come together at the same time, the engine will start.
If not, you've hopelessly flooded the engine and filled the bottom plugs with fuel.  They won't fire.

As a result you have hundreds, if not tens-of-thousands, of pilots creating their own starting technique.  Some stick their tongue out the left side, some the right side.  Some say hail Marys, some sacrafice goats.  Some prime twice.  Some prime 4 times.  And, cracking a throttle 1/4 inch is just a guess.

Priming:  Just in case you didn't know, only one intake valve is open at any given time.  Pumping the primer squirts raw fuel into intake port near the valve.  The open valve has some fuel squirted into it.  The rest of the raw fuel runs down the intake tubes (you have no idea how many intake tubes I've seen that are full of fuel deposits) and into the intake plenum on the bottom of the engine.  On a Cheetah, the fuel will run out of the carb and into the airbox and drip on the ground.  On a Tiger, it'll puddle in the intake plenum. With any luck, it evaporates and makes a mixture that will start the engine.

There is a better way.

Background:  My first plane was a 1977 Cheetah, N9988U. It was 1984.  88U had just a shade over 700 TTSN.  I had 88U for 15 years.  I learned a lot on that plane.  Being new to the 'airplane world,' I too, started the plane according to the POH.  Most times it worked.  Sometimes it didn't.  It was frustrating to be at an 'away' airport and have the engine not start. I began experimenting with starting techniques.  Here is what works EVERY TIME.

How to start an engine:  You may or may not believe it but, your engine wants to start. Under 90% of the conditions you'll encounter, if you use this technique and you are patient, the engine will start.

Any OAT above 40°F to 50°F.

Step 1: Throttle CLOSED

Step 2: Mixture RICH

Step 3: Mags to BOTH

Note (1): The fuel-air mixture will be too lean to fire. You don't need to be concerned about a kickback; especially on a cold engine.
Note (2): On a HOT engine (quick turn around after fueling), hold the starter button down until the engine starts.

Step 4: Be patient

Here is where pilots worry their plane won't start. You aren't starting an XT5 Cadillac with direct injection.

Besides, you really want to get the oil circulating even just a little before you start.  There is nothing that makes me cringe more than to watch a pilot Prime (over prime), crack the throttle, and have the engine start on the first blade and rev to 1200 rpm.  Every moving part in that engine is still waiting for lubricating oil to protect it.

Step 5: Throttle closed, Press the starter button

Remember, you are NOT starting a Cadillac. The engine will turn over several blades before it is ready to start. 
You are pulling fuel from the IDLE circuit (in the carburetor) into the intake manifold.

When the engine starts, gradually bring up the RPMs to about 800 RPM.  Let the engine begin to warm up.

You'll get so you know when to expect the engine to start.

Any OAT between about 30°F to 50°F.

Do the same as above with the following exception

If the engine doesn't start when you expect it to start, pump the throttle one or two times WHILE CRANKING the engine.
Be sure to bring the throttle back to the closed position. 

The reason you pump the throttle while cranking the engine is to spray atomized air into the intake from the accelerator pump.