Mercury 7.5 HP 1969 Spark Plugs - at end of season

[tpenfield]

The boats came out of the water yesterday and I am checking the plugs on my 1969 Mercury 7.5 HP outboard (serial # in my sig below). I noticed the lower plug was very clean versus the upper plug.





I am thinking that I am getting water in the bottom cylinder, since the plug is so clean versus the upper plug.

Thoughts? :noidea:

I could do a head gasket over the winter . . . if I can get one for this engine (???)

Overall the engine runs great, starts right up, idles well, goes very fast (takes my 8 foot pram dinghy to about 15 mph GPS). The only funny thing I notice is a mis-fire or knocking sound at a fast idle under load. I thought it might be a timing issue, but based on the plugs, maybe it is water.

The top of the cylinder has a few spots where carbon deposits have flaked away, but there are also some on the upper cylinder as well.

 

[Scott Danforth]

yes, you can still get parts for the motor, however I would pull it apart, then get all the gaskets needed on one order. probably $15 worth of gaskets and $10 worth of shipping. it may be easier to pull the whole power head and work with just the power head on a bench than attempting to pull the head in situ