Classic signs it's time to de-carb

[steplift20]

Sounds familiar to me I had the same thing happen to my Mercury, I would be driving then the RPms would cut in half and my oil alarm would sound that happened for about a month Running great than RPMs would cut in half, what it turned out to be was I have two power packs and the one that the alarm was hook to would stop working causing the RPms to drop if it happens on land check for spark your probably losing half your sparks to the plugs Like spare said check your power packs Good luck