we have a 650 mercury, its been stood a few years since new gearbox and impellor fitted , it starts well, pumps water etc well, when running in under load [at sea] it seems to suffer a fuel problem, looses all power coughing and spluttering, if you knock the throttle off, then back on gradually,it gets its power back for a short time [ very short time] then looses power again, any idea`s.
