Reply To: 1958 envinrude 35 HP big twin running rough

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November 21, 2018 at 8:55 pm #154514
chris-p
Participant

    I was thinking along the same lines as Frank.

    However, first, start with the basics.

    What is the compression, cold and dry?

    Does the spark jump a 1/4″ gap on an adjustable inline spark tester?

    Most Big Twins of your Vintage should fall in the 90 to 110 psi range. If so, and you have a bright blue spark that jumps a 1/4″ gap, I would look at your exhaust gasket, head gasket, etc… for water intrusion.