The following advice as well as the warning are from Mike Radomsky from some while back.
The easiest way to guarantee an easy hot start is to leave the mixture control alone on shut down. Just kill the engine with the mag switch. Leave the mixture control whereever it was before the shutdown.
On restart, just turn on the boost pump and note fuel pressure and hit the starter. It should start instantally.
Here is the hazard: You are leaving the plane in a potentially dangerous situation. The hazard is that somehow the ground connection to the two mags that was made when you shut off the ignition switch might somehow fail and someone could then pull the prop and get the engine to start.
As a result, this technique is only usable where the plane is going to be left in a relatively secure location, hopefully where you can keep an eye on it.
You do know that the ground connection to each mag was good when you shut off the engine, since when you turned off the ignition it stopped.
I find that the old habit of pulling the mixture control at shutdown can be very hard to break and sometimes I pull the mixture when I know that there will be a hot start in the near future.
A few additional points:
(1) I have an SR22 with the IO550. However, both engines are fuel injected and both share the same problem. When a fuel injected engine is stopped by pulling the mixture, all of the fuel that was in the plumbing from the mixture valve on is gone and has to be replaced before the engine will start.
(2) There are other techniques as described in this thread. However, the one that is dead simple is to just shut down with ignition and leave the fuel alone.
(3) It is possible from engine heat to radiate inside the cowling to the point where the fuel in the suction side of the electric pump turns to vapor. If the day is really hot where the ramp is just radiating heat and you are at a relatively high altitude (>1000’ even) that fuel may vaporize. In that case the electric pump won’t pump and the techniques described about running the electric pump won’t help.
Here is what to do to fix the vapor where the electric fuel pump won’t pump: (a) Take the keys, put them in your pocket (b) get your fuel sampler © station someone at the fuel pump switch (d) get to the gascolator under the engine (e) get that person to hit the “prime” switch (f) keep taking samples until you get liquid fuel in the sampler. You will probably hear the pitch of the electric pump go lower when the liquid fuel gets to it.
Here is what to do to avoid the problem to begin with: (a) park facing the wind if possible (b) right after shutdown open the oil filler door. You will probably feel the stream of very hot air exit the cowling. With air circulating through the cowling, the tendency of the engine to heat the fuel lines to the point of vapor will be less and you will probably avoid the problem. If not, see above for the fix.
Finally, don’t overheat the starter. I can’t remember what the POH says on the starter use, but follow that. Let it cool between attempts. If you follow the shut down by ignition technique, you won’t have a hot starter problem.