1985 Mercury Outboard V-300 V-3.4L Shop Service Manual, Page 65Get this manual
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Testing Fuel Pumps I nstall clear fu el hose(s) between fu el pu mp and carburetor(s)Run engineand inspect fu el passi ng th ru hose(s) fo air bubblesIf air bubbles are found, seeAir Bubbles in Fuel L