1978 75 hp johnson

[Set44]

Boat bogs and doesn't plane out. Carbs are clean and rebuilt with new kits. Compression has been checked 124 psi cold. New power pack and new coils. A friend who I thought was a good at working on outboards told me to gap plugs at 0.040. Did a internet search to find out the correct gap is 0.030. Could this be the reason boat is missing at 2500? Any help is greatly appreciated nearest marine is over 100 miles. local marine is closed dew to pandemic. Owner is in bad health.

 

[F_R]

I realize I am overly pessimistic, but I immediately think water intrusion into a cylinder.

 

[racerone]

Does spark jump a gap of 7/16" , yes or no.-----Did this issue develop suddenly ?-----How did it run last year for you ?

 

[Set44]

I tested the spark gap. 7/16 yes. The resistance on the staror test higher than limit. Did same thing last year. It ran well in spring when air temps where 60° f. Late June came temps went into high 80's the issue happened. I rebuilt carbs in the fall when the temps came back down boat ran fine. Boat ran fine this year until the temps climped into to high 80s and 90s.
Plugs are not milky no cloud of stream. Also removed plugs on the lake today no sign of water on plugs or any rust. If that helps.

 

[racerone]

I would be looking into changing the idle orifice plug.----Part book shows it as a #32.----I would try a #34 and test run on a hot day.

 

[Set44]

I would be looking into changing the idle orifice plug.----Part book shows it as a #32.----I would try a #34 and test run on a

I would be looking into changing the idle orifice plug.----Part book shows it as a #32.----I would try a #34 and test run on a hot day.

Was looking into changing the idle orifice plugs, like you said. Discovered my carbs have #30 should I replace them with #32?