1975 mercury 115 HP

Discussion in 'Bubba's Outboards' started by crackers, Jul 8, 2009.

  1. crackers

    crackers New Member

    Messages:
    296
    State:
    Arkansas
    got a mercury that i pulled the top spark plug and it had some small bits of alumium on it and causing it to not fire this has me very worried. from what i can find out about where the alumium came from it is I think from pre-detonation what ever that is I caught this early and the piston looks to be in good shape and the cyl compression is at 120 lbs. but Im at a loss at what to do next. dont want to take it to a outboard mechanic. without some of you ppls very good advice of what to do next....and has any one had this problem before.
     
  2. tbull

    tbull New Member

    Messages:
    3,318
    State:
    SW Ohio
    What were the compression numbers on the other cylinders??? Best to pull the head on it and get a good look at the cylinder walls asap. How did you look at the piston? Through the spark plug hole? If so alot of times the head of the piston may not look bad, you have to pull the head in order to get a good look at it. Just from a prior mishap I had, the spark plug threads were stripped, pieces fell into the cylinder and chewed up the piston head pretty good, and put some nice grooves in the wall. If you do pull the head, try and post some pics on here. Thats something you want to get figured out asap IMO...
     

  3. crackers

    crackers New Member

    Messages:
    296
    State:
    Arkansas
    checked all cyls and they checked out ok at 120 to 125, the aluminum came from burn off from the top of the piston, comes from pre-detonation. (this is from what i read from the internet, and if you read it from the internet its got to be true). and thinking its not my fuel its got to be the firing. so I pulled the distribitor and found moisture in there and was causing it to cross-fire. this afternoon,cleaned it all up. Put the water muff on and it fired right up and sounded real good.I had reset all the floats a few days ago and they were good. so with the water-muff on Ill hot shot it with some Stable and gas-mix from the tank. then take it to the lake for a run. will pull no. one plug in the morning to look at the cyl. just to make sure its ok. the distributor sets upside down in this engine so the plug wires are screwed in to the distribitor cap. going to get me some silicone seal in a spray can and spray it on the distribitor cap so this wont happen again... I took a picture of the plug before i cleaned it up and will post it as soon as i can learn how to post a photo.
     
  4. crackers

    crackers New Member

    Messages:
    296
    State:
    Arkansas
    pulled no. 1 plug and it looks very good and the cyl. looks very good from looking down the hole with a lite. I found out with an outboard dont take nothing for granted. this is a learning experience as well as fixing an outboard...going to the lake now to try her out