Spark Plugs For merc 20hp

Discussion in 'Bubba's Outboards' started by miichael, Nov 30, 2006.

  1. miichael

    miichael New Member

    Messages:
    380
    State:
    North Carolina
    Hey I currently been using the spark plugs that my motor calls for but i was wondering if i could use a different type of plug. The ones it calls for you cant gap but id like to have a plug that i can gap so i can gap it little wider for low idling. Its a 1976 Mercury 20HP.
     
  2. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    You'll take the chance of hitting the electrode with the piston.

    Those surface gap plugs are for a reason. They'll help dissapate the heat of the cylinder much quicker than any other plug.

    Along with your water pump, the heat range of the spark plug plays an important part in engine operating temps.

    For idling purpose, you'll want your carb in the best condition possible and your engine interior as carbon free as possible. It won't stay that way long. Idling is one of the worst ways to operate an engine for any length of time, but when you gotta troll, ya gotta troll.
     

  3. miichael

    miichael New Member

    Messages:
    380
    State:
    North Carolina
    My evinrude takes the same type plugs and i been using just a standard plug that a guy recommended gapped at .40 and it made a huge difference. Is there something different on the mercury that wont allow you to use the other plugs due to clearance issues?? i was worried about using the other plugs in my evinrude thought they may hit but it sure made it run a lot better. It calls for UL77V plug but i been running L77J4 in it the past 2 years. Should i not use them in my evinrude? I know the plugs that you can gap sure gives a lot better fire and less fouling
     
  4. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    I never engineered these engines. I just go by factory specs.

    If you brought that engine to me to fix, the first thing I'd do is throw out the wrong plugs and put in what's called for.

    If however, another plug was spec'd as an alternative, that'd be cool with me.
     
  5. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Michel My orignal shop manuel on the year and h/p says to use surface gap plugs only. On the smaller one it gave a gap type plug but on the 20 and up it said surface gap and that would be

    AC-V40FFK

    Champion- L78V
     
  6. miichael

    miichael New Member

    Messages:
    380
    State:
    North Carolina
    What about 1974 70HP evinrude. On the engine itself it says use UL77V and the guy at marina told me to run L77J4 in it gaped at .030 or if i was running real low rpm i could gap at .040. Is the evinrude safe to run the different plugs and mercury isn't? Been running L77J4 for 2 years.
     
  7. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    On the evenrude you will be fine with that gap plug.
    If it was my evenrude I would use QL77JC4 in it and gap them at 40

    On my mercury's I have I run NGK plugs and get good results from them on idle and WOT
     
  8. miichael

    miichael New Member

    Messages:
    380
    State:
    North Carolina
    Great sounds good. Ill just use the plugs that the mercury calls for then.
     
  9. vegasryder

    vegasryder New Member

    Messages:
    324
    State:
    illinois

    You can always measure the clearance at TDC if your willing to risk using anything other than the plugs specified.All you need is a caliper and a piece of wire(soldering or paperclip).