I used to rebuild Evinrude Mariner and Mercury outboards, that included spraying them, 90% of the time I used cellulose spray cans.
The first coats should be done very quickly and very light so they dry off fast, I always tried to warm the cowl with a hot hair paint stripper (carefully).
Several primers/undercoats, let it cure for a couple of days and the top coat can go on wet without many worries.
There were some Evinrudes that were a nightmare, not sure what the original coating was but they were a swine to stop reacting, it was usually the 15hp models for some reason.
if its already painted and the paint isnt cracked or falling off, then just key it with 800 wet n dry and a couple of coats of rattle can primer , sand again with 800 until its nice and smooth then on with some paint
if its bare fibre glass , or the old paint is terrible then i would use etch on the bare stuff , then as above