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Mercury 7.5 Difficult/Impossible Start

Oil Gypsy

New member
Hello, I’ve recently acquired a early 80’s Mercury 7.5 outboard, the unit is in immaculate condition having been in storage for many years, unfortunately it wasn’t properly prepared for long term storage, the gas inside the had evaporated and left a yellow deposit through the fuel system. Since owning the motor I’ve cleaned and rebuilt the carb with all new gaskets and a new float, replaced water pump and housing with all new gaskets, replaced gear selector seal in the lower leg, refilled the leg oil. I’ve metered the coils and have 960 ohms on each coil and 5 ohms from spark plug cable to earth. Inspected the rear ground cables which are good with no corrosion. The compression is 120 in both cylinders. The spark plugs were changed and gapped at 30thou and I have a good spark on each plug. I have a new tank and fresh fuel. The motor is impossible to start normally, I can get it going with starting fluid quite easily and it will then run and idle perfectly, it will restart after 15 – 20 minutes but after that it requires starter fluid again. I’ve run Seafoam top end cleaner through the carb while its running, this produces plenty of smoke and bogs the engine down, shortly after the seafoam spray is stopped the motor runs normally. When puling the cord turning it over it does appear slightly stiff, not as easy as my 15hp, I’ve put this down to the high compression. I’ve more or less run out of ideas to make it start reliably and any suggestions would be appreciated.
 
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