1978 mercury 80hp,model 800,2 out 4 plugs not firing.

[felderlostnspace]

the bottom 2 spark plugs are not firing while the motor is running.while turning the engine over all 4 plugs fire,but once cranked the bottom 2 plugs stop firing.i took the top two coils and swaped them with the bottom 2 coils,but the bottom 2 sparkk plugs still not firing,so that tells me that the coils are ok.i have checked the wiring from the switch box to the coils and that seems ok.i guess the switch box or stator may be bad.any help would be great.i am lost and my boss(my beautiful wife says no more money will be spent)please help me.which way should i go.thanks in advance,Bill

 

[WillyBWright]

Re: 1978 mercury 80hp,model 800,2 out 4 plugs not firing.

Are you sure the spark is going away, or might the bottom carburetor have a problem? That would prevent that motor from running on the bottom two as well. If the spark is going away on two, it probably means that it's weak on the two that manage to fire. Could be stator, could be switchbox.<br /><br />You can tell with one of these and a manual... Merc Multimeter, or one of these if you have a compatible multimeter... DVA Adapter. I know it's a bit of an investment, but if you bought the wrong component and had to buy the other, you'd have saved money by buying the instrument and nailing down which part is at fault. You can't return ignition stuff. Either part cost more than the meter, and you can use it anywhere you'd use a multimeter. It might even tell you that both parts are fine.<br /><br />I'd put odds at 50/50 for either part failing. Those stators were usually okay, but the wires leading from them have problems with the insulation rotting and falling off.<br /><br />It could also be a flywheel problem. If the magnet laminations get rusty, magnetism drops off sharply.

 

[felderlostnspace]

Re: 1978 mercury 80hp,model 800,2 out 4 plugs not firing.

thanks for the reply.i just turned the motor over,it is night here so maybe i could see if i had spark grounding some where.i did not see any.i turned the motor over and all plugs are firing.i can finnallyget the motor running but it is skipping.i again check the plugs for fire with engine running.the 2 bottom plugs are now not firing.i can pull the top 2 plugs wires off seperately and the motor skips worst and they are firing.when i remove the 2 bottom plug wire seperately there is no change in the running of the motor.does this help where it might pin down the problem.if you still think it might be the switch box or stator,i'll purchase a meter tommorow and check them.thanks again for the help.any ideal would be great.thanks,Bill