problem with 6hp 1990 power problem

[snowblind]

hi first it's a 2 cylinder 1990 6hp,and when i go with my outboard, when i run and at about 20% of the gaz power, the engine is going down instead of keep going up and faster, and is not stable. my hose to the tank is correct,can it be the gaz filter? or what...
i don't know if it can help, here's what i did.
in the beginning the outboard was ok.
i had gaz of 1 year in my tank. one time ,i connect my hose in reverse(by mistake) and pump and pump.change the hose in right direction, and 2 days later , problem begin, don't know if it's related.
i ran the outboard 2 days like that with my problem. my 6 hp was like a 2hp.
anybody can help me.
thanks

guy

[boats.net]

It may be a clogged carb, if it hasn't been run much for awhile then the carb may need to be cleaned.