1985 Mercury Outboard V-300 V-3.4L Shop Service Manual, Page 83Get this manual
FUEL TANK MAINTENANCE
Th inside th fuel lank should be cleaned nce each seaso nDin or water ma have entered Ih fuel tank during refilling and collected at the ha ll of th fuel tank ean th tank by flu shing with clean leadfree gasoline or kerose ne Fuel Tank Components
If uel restriction problem is nco untered it is possible Iha fue lank fi ller on end of utlet tube is obstructed Re move cover from fue ta nk and inspec filter (Figurefor varn ish, dirt or gumm deposit sClean filt er by rinsing in cleanlead free gasoline or kerosene