Below are the steps for starting the IO-540 from the Lycoming Ops manual. They recommend the same procedure for hot starts as they do for cold (see last note). Kind of surprised by this.
In my plane, I’ve found that their recommended cold start procedure doesn’t work well for the first start of the day, but it works really well for hot starts. For my plane, I consider a hot start to be anything after the first run of the day up to 4-5 hours after the first flight.
For cold starts I use: throttle 1/2 travel, mixture rich, fuel pump 3-5 seconds, throttle cracked 1/2”, engage starter. After start I usually need to pull the throttle back a little to get the desired idle RPM, and I always lean it for taxi after starting.
As mentioned earlier, each engine probably has some nuance that requires experimentation. It took me quite a while to get hot starts down in my RV-10. The key for my engine is to leave the mixture in ICO position until the engine fires. On some starts this can seem like a long time, but if I move the mixture too soon it never fires.
FROM THE LYCOMING OPS MANUAL
“Page 3-2 b. IO-540 Series (Cold Engine).
(1) Perform pre-flight inspection.
(2) Set propeller governor in “Full RPM”.
(3) Turn fuel valve to “on” position.
(4) Open throttle approximately 1⁄4 travel.
(5) Turn boost pump on and move mixture control to “Full Rich” position until a slight but steady flow is indicated.
(6) Return mixture control to “Idle Cut-Off” position.
(7) Set magneto selector switch. Consult airframe manufacturer’s handbook for correct position.
(8) Engage starter.
(9) When engine starts, place magneto selector switch in “Both” position.
(10) Move mixture control slowly and smoothly to “Full Rich”.
(11) Check oil pressure gage for indicated pressure. If oil pressure is not indicated within thirty seconds, stop the engine and determine trouble.
NOTE
If engine fails to achieve a normal start, assume it to be flooded. Crank engine over with throttle wide open and ignition off. Then repeat above procedure.
Hot Engine – Because fuel percolates, the system must be cleared of vapor; it is recommended that the same procedure, as outlined on page 3-2, be used for starting a hot engine.”