If in fact it overheated , you need to do a compression test.-----Post the numbers here.-----A " new to you " motor should always start the next life with a new impeller.
Checked flywheel key ?-----Does spark jump a gap of 3/8" or more?-----The passages are the oil recirculation circuit.----They are not involved with the " no start " issue for you!----Switched plug wires ??
Remove bypass covers and look at pistons and rings.----Nozzle gasket is a donut around that tube sticking out of carburetor body.---Remove bowl to find it.
Does spark jump a gap of 5/16" on both leads , yes or no ?----Post the actual compression test values you have.----Nozzle gasket is in place ?----Checked reed valves ?
Tested the overheat horn ??-----Installed a new impeller when you got the boat ??-----Inspected / cleaned the carburetors ?----If unit sat for years the carburetors could be gummed up.
Note ----The battery is not used to make voltage to fire the sparkplugs.----All done by the spinning flywheel and electronic bits.----There are numerous wires and connections that could be faulty.----Causing the intermittent spark.
