Well said DD, as you would know about starting hot engines especially the IO540 (Lyc).
I am NO expert, but do have significant time flying both the Lycoming 540 and the Continental 520 engines, I don't mean to preach (especially to those who already know) but to have an understanding of the engine manufacturer will help you with your choice of starting techniques.
The two engines of choice for the 6-8 seat single have traditionally been the
Lycoming IO-540 (and its many variants TSIO etc) and the
Continental IO-520 also with a few mods and derivatives.
Lyc engines have the fuel injection nozzles in such a place that the fuel (vapour) is sprayed directly onto the back of the intake valve. When you prime you get lots of effective fuel (vapour) in the immediate area of the valve and at least one cylinder gets a good shot of fuel.
Therefore over priming floods the engine. When starting you need to take away a lot of the fuel (vapour and liquid) before the best mixture is obtained in the cylinders for the spark to be able to ignite it. In other words the engine seems to crank for a few seconds before it fires. Then reintroduce the fuel with the mixture control.
This is why you start in ICO (idle Cutoff) so no new fuel is introduced which will guarantee a flooded start.
This is also the preferred manufactures start method. ie With the Mixture rich for only a short (3 sec) prime, them Mixture ICO until the engine fires on start.
For a HOT start the engine should NOT be primed. Ie the fuel pump should only be run for a very short time (to pressurise the fuel lines) with the mixture in ICO (no fuel flows to the injectors) as the fuel vapour already present after the shutdown will be sufficient to get a start.
Continental 520 series engines have the injector further away from the intake valve. In this case fuel (vapour) tends to sit back from the valve. When cranking (low suction) only floating vapour in the intake can get into the cylinder and ignite. This is almost opposite to the Lyc engines and means you need lots of fuel to get the engine to fire. The continental engine need mixture rich and really decent prime to get a good start.
HOT starting the conti. engine is done the same as for a cold start but you do have a higher chance of a "Vapour Lock" occurring.
(Vapour locks occur in all of these type of engines, but the Cont. 520/470 seems to be the most common to see it)
Simply a vapour lock is caused when the warm (hot) engine creates a low density of air in the manifold, the suction in the cylinder has trouble moving this low density air containing fuel vapour into the cylinder, and the air that dose make it has a very low effective mixture.
The answer is to prime the engine a bit more, and as the manufacturer recommends you can use the primer during start to boost the fuel/air ratio to achieve a start.
Most Conti. engines exhibiting a vapour lock will start, then die (use up the available prime fuel) so you need to give it a good prime, and then when it starts to die (tickle it) until it is self sustaining.
CAUTION as over priming during start can and WILL cause induction fires (a fire in the induction manifold) or in the engine bay (as the over primed fuel leaks into the engine bay from the manifold drains).
This is why you should NEVER delay a start after fuel pump priming (Always Prime, Clear Prop and Start within a few seconds).
Having said ALL of the above, all engines are slightly individual and while many different methods DO work it is best to use the method given to you by the aircraft/engine manufacturer.
CHADZAT while this question gave me and others a good chance to dribble on for a few pages, the only real question to ask is "Where is the POH, mate"
Have fun the Debo is a very nice thing to fly.
Richo