74 40horse top plug fouls

[58 Shell Lake]

I have a 1974 40 horse (mod#40454S) with fresh plugs it runs great for 10 or 15 min then top cylinder drops out. if i pull the plug it dosent look bad but when i spin the motor there is no spark. no amount of cleaning will help, I must put in a fresh plug to regain spark. Replace coils,points,condensors, same results. both cylinders have 90lbs of compression and don't leak down. a 40 horse on 1 lung dose not a 20 horse make! oh and even on 1 lung she fiers right up.

 

[tashasdaddy]

Re: 74 40horse top plug fouls

i would say you either have a coil going bad, or a dirty carb flooding out the top cylinder. which is not possible, as you only have one carb. while you are fiddling with the plug, the coil is cooling off, and works again. swap places with the coils, see if the problem goes to the bottom cylinder.

 

[58 Shell Lake]

Re: 74 40horse top plug fouls

I have tried both NEW coils in both positions, Same prob. This was my original problem so i did the Massive tune up, and same results. I'm thinking about a new gasket set and rip the thing apart and just regasket everything. Its only about 100 bucks. my local boat shop said it could be a bad gasket next to a water jacket sucking water into the cylinder and taking out the plug. I just don't know. The motor has never been in salt water just in case it might matter to help figure this out.. Thanks

 

[F_R]

Re: 74 40horse top plug fouls

Whoa, hold up there. That's getting kind of extreme when you haven't even diagnosed the problem.

You say "no spark--regaining spark". Are you talking about spark across the plug gap or spark off the coil wire? If you have no spark off the coil wire, you have a definate ignition problem. But if it is the plug that is shorted out, it could be water or a half dozen other things.

If you determine that it is shorting plugs, It may be the fuel pump. Without looking, I don't know which cylinder the pump is mounted on. If it is the top one, unbolt it from the cylinder and give the squeezer bulb a mash. If gas squirts out the pulse hole in the pump you have found your problem.

If it is a water intrusion problem, there should be water droplets on the plug. I'm going to tell you something here that I do not reccommend because there is extreme danger of fire. But I remove the plug and securely ground the wire away from the plug hole. Then start the motor and hold a piece of glass or mirror in front of the plug hole. If there is water intrusion you will see droplets of water on the mirror, along with oily fuel. WARNING! I told you there is danger of fire, so "don't do as I do"----etc