Only reason I tape them is, I feel the loss of water out the low water pickup could starve the water pump of sufficient water flow to not damage the pump or adequately flush the motor. Just a personal thing, may be unnecessary, but I'll continue to do it. Not a big deal to tape it, flush it, then remove it.
I don't know about the Yamaha until I try it. The Merc works just fine, I have a pressure gauge on the monitor and the pressure is the same with the hose as when idling in the sea.
I'm not concerned about overheating the engine, that will not happen at idle even if only a mall amount of water gets in the cooling system, keep in mind outboards run very cool temps cars run a lot hotter and overheat alarm will go off. My main concern is the water pump life if you run it dry you kill the impeller quick. I don't run it in sand or mud and change at 500 hours ( complete pump) still like new . I have to say Optimax Mercs (200 hp up) have big water pumps . I monitor water pressure, if I notice it dropping bellow normal even a little I will change impeller or even complete pump.
I think I will tape the front pick up on the Yam as well, like you say only takes a minute and no harm as long as you take the tape off when finished. On the Merc when you turn the hose on water runs from the front holes but as soon as you start it stops it seems all the water gets sucked .
