1986 75 hp merc 4cyl

Discussion in 'Bubba's Outboards' started by dieselcat, Jul 22, 2008.

  1. dieselcat

    dieselcat New Member

    Messages:
    406
    State:
    Washington, Mis
    I was wondering if anyone knows what compression ratio my motor is supposed to have? thanks in advance
     
  2. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Anything from 90# and up will work as long as each cylinder is within 10% of each other. That is the key to good compression. If one is at 90 and two at 115 something is wrong and needs to be corrected An engine will run good at 80# of compression as long as all cylinders are at close to 80 it will be just hard to start.

    Take all the plugs out and open the throttle wide open and check each cylinder and write it down for future referance and when you are through do a good decarb and I bet you will raise the compression somewhat.
     

  3. dieselcat

    dieselcat New Member

    Messages:
    406
    State:
    Washington, Mis
    cyl 1 70# 2 and 3 are 75#,we couldn't get to #4 to check it so dont know what it is