25 HP Honda outboard - stalling

So my organization uses a 25 HP Honda outboard on an inflatable dinghy. As of late, it continually stalls out at low speed, and only runs well with about 3/4 choke. I've drained out the fuel/water filter multiple times, as well as the little filter inside the engine. Idle screw and the carburetor set screws are actually too high, and yet it still stalls out, feels like it's fuel-starved.

I've swapped out fuel tanks, but it's possible they both have bad fuel. My only other move is to gap the spark plugs, but everything seems to point to a fuel problem. The engine runs great at high speeds, planes with no issues, but whenever you use it under load (i.e., a lot of people in the boat or towing/pushing something) the performance just degrades more and more.

Ideas/suggestions needed. Help.

Re: 25 HP Honda outboard - stalling

I`m no expert on outboards but i`ve been a bike mechanic for almost 40yrs and these Honda 25`s are more or less a bike engine laid on it`s side as i own one myself.

As it`ll only run with the choke 3/4 out at low speed but runs fine higher up then it sounds like your carb pilot circuit is blocked and is restricting the flow of fuel. Using the choke reduces the amount of air getting into the system hence making the mixture richer so in your case to the correct level so it`ll run. I`m afraid to say that unless something like a liquid carb cleaner added to your fuel won`t clear the problem then it`ll be a case of buying some new gaskets and stripping the carbs off and giving them a really good clean and blowing out the passages with compressed air or a tin of carb cleaner.

Cheers, Matt.