Originally Posted by Bill Boyd
Re the Lycoming unofficial procedure:
What does the brief rich mixture setting (step 5) with the boost off and the engine not being cranked accomplish?
For my M1B, it floods it more and won't start.
If it is hot and I stop at the pumps.
To start , remain at ICO, boost maybe but start at ICO and then open the mixture. it is a multi handed procedure with some feathering of the mix as initially it is full of vapor, then at full rich it will flood and kill the engine if not at 1200+ rpm blasting everyone around.
I my head, its like this . .
The lines have vaporized all the fuel and it is in the bottom of the cylinder or down in the intake tubes, all vapor.
Throttle open 2"ish, mix untouched at ICO, the engine begins to rotate, the rich vapors don't fire and rapidly the A/F drops passes into happy zone, suddenly the engine roars, (tiny throttle techniques have failed me) Drop the throttle to a lower roar while opening mixture. a rapid movement about 1/3 then as needed, but no more than 1" out. ( I am set rich at idle anyway another story) If the engine is dying, massage mix and throttle and as last resort - tick the boost to catch but that is rare, mostly just pump the mixture to full then back to clear the vapor. I leave at 1000-1100 rpm a few seconds (10?) to clear and then drop to normal idle with about 3/4" out. YMMV for sure.
In very cold temps with negative density altitudes this engine will run lean, then when advancing throttle for TO it will stumble and then after passing the idle circuit will blast to full power like an old 2 stroke on the pipe. So the idle mix was set when quite cold leaveing the remainder of the temperatures too rich . . meaning I keep a rich-minus-3/4" setting when dropping throttle in flight unless at TO. This way I don't get so much spitting on the belly from the sniffle valve on hot days. Warm engine taxi is always with mix out 3/4" (or a little more).
Maybe after having to learn each (non-EFI) engines quirks and doing them for 60 yrs it has become a natural (and acceptable) habit. But . . .
. . . that SDS sure is sounding nice by this
Oly, that purge valve has been considered but there we are, another knob to fiddle with.
Larry, my friends IO540 starts with that procedure just fine too. But one day he was with and offered the technique. Did not work for my install, so no perfect procedure, experiment and listen to the engine and respond, accepting that actions can have a delay.