1975 Merc 402 problem

[73ouachita]

I have a 1975 Merc 402 that only runs when engine is cool. I have had it to a boat mechanic 3 times and he has replaced everything in the fuel system and he continues to tell me the boat is fixed and every time I go to the lake (an hour away) I am left stranded in the middle of the lake. I have already paid the guy 300 bucks and I am convinced he just doesn't want to mess with it. The motor runs fine out of the water but I cannot rev it to full rpm without having it in the water. It also will start fine and run when you first put it in, but when you go to plane it out it bogs down and dies, and then will not restart for an hour or so. I am at my wits end here and really need some help, since it looks like I'm gonna have to fix it myself. Someone told me the stator might be bad??? Any info will be greatly appreciated.

 

[green4themoney]

Re: 1975 Merc 402 problem

hmmm maybe its overheating? have you had the water pump replaced?

 

[eldplanko]

Re: 1975 Merc 402 problem

Check to see if you're only running on 1 cylinder. Check both plugs for spark. If they both have spark, unplug the lower plug and try to start. If it runs, shut it down, and try to run with the lower plug pluged in and the upper plug unplugged.

I had the same problem, turns out I was getting water in the lower cylinder.

 

[73ouachita]

Re: 1975 Merc 402 problem

I checked for fire in both cylinders and I'm not getting any spark to either cylinder, but only after the engine is hot. When the engine is cool, I have good spark to both cylinders. Im thinking either bad coils or bad stator? Don't know which one it could be.

 

[73ouachita]

Re: 1975 Merc 402 problem

I am also sure that it's not overheating. I just replaced the impeller and haven't put 2 hours on the motor since. And my tell tale stream is good and strong through all rpms when the motor is running.

 

[jjbarnes]

Re: 1975 Merc 402 problem

Your problem sounds like it might be bad coils. If they are cracked, they will run ok cold but will fail when they heat up and expand. You'll monkey with everything you can think of while the engine is cooling down and it will suddenly start running again and you are led to believe you fixed it by doing something totally unrelated (cleaning the carb, filter, etc.) until it gets hot again. I had the same problem on a Johnson until I replaced the coils. If the casing or cover is cracked very much it may be bad.
The stators don't really go bad as much as their wiring just fails. If you go that route please let me know how you aquire one and at what price. Best I've found is $175. I have a '73 merc 402 with seriously rotten wires and need a new stator because they are sheared off at the base.
Hope that is atleast some help.