1985 Mercury Outboard V-300 V-3.4L Shop Service Manual, Page 63Get this manual
POlilble Ceuse Reed block housing loose, or gaskets are defective Improperly routed or restricted bleed hose (s)-
Corrective Action Using pressure oil can, spray 2-cycle oil around reed block housing crankcase housing matching surfaces and carburetor baseIf engine RPM changes, tighten or replace reed block housing gaskets or carburetor base gaskets, as neededRefer to "Reed Blocks-Reassembly and Installation" in "Power head" section