Water ingress/misfire

[zaskar98]

On my 1993 175 looper, the bottom left hand spark plug (viewed from rear) (no. 5?) gets rusty and will misfire following coming off plane when powerhead sits pretty low & water backs up. Looking inside case there is a small hole below this plug that looks like it may be a drain and I think this is where water is coming in and causing a short/misfire, also some salt deposits on cylinder head around this area (temp cure with the magical properties of WD40). Can this drain hole be blocked off, or should it have a grommet in it in the first place (looks pretty clean, so one may have dropped out)

 

[Kenneth Duke]

Re: Water ingress/misfire

There are several causes for this problem.But one of the most common one is a blown cyl head gasket. Remove that head some times the condition of the gasket will tell you where the water is coming in at.Check both Head surface and cyl block surface for warpage.check these first and keep us posted.

 

[zaskar98]

Re: Water ingress/misfire

Thanks for the reply Boatmec, but I think mustn't have been clear in my original post; the rust is on the outside of the plug, hence my suspicion of seawater getting inside the cover. How high should my motor be? Currently when on the plane, the foil sits right on the surface of the water, and I only get a bit of ventilation in tight turns. Would raising the motor to get the powerhead higher be possible? Is that a drain hole in the bottom of the case just below the offending plug or should it be blocked off? I've checked through the Clymer manual but can find go guidance there>

 

[Mark42]

Re: Water ingress/misfire

I don't know your specific setup, but I would think that a few simple tests would help diagnose the problem.<br /><br />How about wrapping the rusty plug with dry paper towel and make the manuvers that you think are causing water to enter. Then check the towel for water. You can put a piece of duct tape over the hole and see if the problem goes away. A service manual should show you if there is supposed to be a fitting in that hole or not. <br /><br />I suggest trying one or all of the above before taking any repair/disassembly action.<br /><br />Just some thoughts. Hope they help.<br />Mark.