if you have replaced the spark plugs and still have the same defect you have to check the ignition system (timing) and then the carb (if it is 2 stroke)
and the last is to check cylinder compression it may be bollow the spec.
In some outboard engines the ignition timing is by adjusting the stator with flywheel mark if available(you have to check) this will balance the advance and retard position with BTDC and must be within the spec.
If you are using the engine for trolling with low RPM and you did not tried full throttle for long period it may be that the exhaust ports are reduced/blocked due to carbon deposits and will affect the engines performance
Probably the fuel filter or maybe fuel pump. Closing the choke reduces air flow and richens the mix without adding any additional fuel. Check the easy stuff first.. Fuel Filter. If it's good then try squeezing the bulb while its running. If it improves then I would rebuild the fuel pump, it's easy and cheap. If that fails to fix the problem then rebuild the carb or run some SeaFoam through it according to the mixing instructions on the can.
finally got it, there was a bad piece of line behind the starter, not sure what it's for but it was spraying a fine mist of fuel. (don't know how I missed it before) replaced it everythings great now. Thanks for the help.
