1897 mercury 35 hp

[Collinp24]

Ok so I’m at my whits end with this engine . 87 35hp mercury . It will crank up and run but runs rough and any throttle you give it , it dies . Then some days it will crank up and run just fine . The plugs are getting oil on them so I thought it was getting flooded . I replaced all fuel lines (they were old and needed it). Replaced fuel filter , new plugs , removed carb and cleaned it and rebuilt it (new float and everything) . Has 125 compression on both cylinders . Spark is good . Fresh fuel and the correct amount of oil mixture . Any ideas before I drop this off with a boat mechanic ?

 

[fitz73222]

Possible fuel pump diaphragm, worth a check.

 

[fastjeff]

My! That's a really old Merc. (Din't think they built outboards back then...)

Try this: Open the idle mixture jet 1/2 turn OUT (CCW). That's cured your type of problem many times over.

Jeff