The list below is really for situations either you have failed to start a few times or where you know that aircraft will not be easy to start. Having flown regularly with Continental GTSIO-520s, some of the trickiest to start while hot, there was one technique that always works, and works for a very logical reason. It is basically Big Pistons Forever's last suggestion, with a bit more detail.
1. Over prime the engine. Use the aircraft's priming technique, be it a special priming pump, the electric fuel pump or simply exercising the throttle, but do it excessively. Now you know you have an over-rich mixture, not an over-lean mixture.
2. Set mixture to cut-off. Now you know you are not going to be adding more fuel.
3. Open the throttle wide. Now you know you are going to be adding a lot of air.
4. Hand on throttle, crank the starter until the engine fires. The cranking engine draws in air and exhausts the over-rich mixture, weakening the mixture until it reaches the right level.
5. Immediately but smoothly bring back the throttle to a little above idle (1/4" in most aircraft for starting) then mixture up to rich, but don't hurry either action.
I have had a backfire using this procedure, but that was because there was something wrong (can't remember what - might have been a cracked exhaust as that a/c had a few) and did no damage itself; it should not happen. Starts often put fuel in the exhausts, and shouldn't cause a backfire.
Last edited by Flaymy; 23rd August 2012 at 12:38.