90hp merc misfire

Discussion in 'Bubba's Outboards' started by shadguts, Aug 2, 2007.

  1. shadguts

    shadguts New Member

    Messages:
    564
    State:
    Tennessee
    I have a 90hp 1978 merc. I installed the gaskets at water jacket cover and rebuilt carbs the engine doesnt leak any more and starts easy but seems to have an intermitant miss on two plugs. I used a spark tester and #4 and#6 sometimes miss a spark all the others seem to be firing fine. The seloc manual isnt much help here as far as trouble shooting. I took the cap and wires off a 115 merc and still have the same thing. What to look for now? The 115 is the same ignition system no points and one coil.
     
  2. shadguts

    shadguts New Member

    Messages:
    564
    State:
    Tennessee
    I called a local repair and parts store and they quoted me a price for a new distribitor cap alone they said $154.70. Ha! There is no way I'd ever give that for a $15 plastic distibitor cap. Does anyone know of a place online that may have on?
     

  3. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Chris leave me a serial number and I'll see what I can locate for you.
     
  4. shadguts

    shadguts New Member

    Messages:
    564
    State:
    Tennessee
    Thanks bubbacat. The number is 5030488. I checked again and the same firing issue. After moving the cap around a little Im getting good spark on all 6. It seemed to run a little rough and I mean very little on the muffs but I took it out on the lake and it seemed as smooth as glass. I would still like to know about a cap and wires and rotor though. The motor is almost 30 years old and could surely use them. I am sure that it was getting good spark and fuel and the timing is set to specs and i am thinking that the different compression on the one cylinder is the rough part. all cylinders were 155 except one and it was 130. I put a little oil in the cylinder but the reading was the same. It has set for almost three years so maybe a ring issue? Thanks for all your help and advice it is appreciated!