Im at a loss and hope someone here can help. When I first go out and run, for any length of time, the engine runs fine...right up until I throttle down. After I come down to idle or neutral, it starts running rough. When I try to throttle back up, it's sluggish and takes about 30 seconds for it to fully kick in. It'll do that all day until I go back to the dock and let it sit for a while. So far, I've changed all filters, changed the plugs, changed the primer bulb, and ran Sea Foam through it using an auxiliary tank. Using the auxiliary tank served 2 purposes....it also isolated the problem to the engine. What could this be?