1979 mercury 70 hp

[thomas seale]

I bought this boat last fall.It has a 70 hp 3cyl. and it ran fine.This spring, i installed new spark plugs.Took it out again and it idled rough,and was hard to accelerate and motor would die out at slow speeds but would run at full throttle.I pull the plug wires off one at a time.The middle sparkplug is not firing at all.I replace that sparkplug and wire and still not firing.Does it have a bad coil? or is something burning the coil out?

 

[ob]

Re: 1979 mercury 70 hp

Crash,Try swapping out the suspected bad coil with one that is firing and see if your dead cylinder moves.Did you use the recommended sparkplugs on changeout?

 

[petryshyn]

Re: 1979 mercury 70 hp

Check for spark at that plug wire. If none, switch the wires from the pack that go to each coil primary to see if the problem follows the pack or coil.<br /><br />

 

[thomas seale]

Re: 1979 mercury 70 hp

First of all i would to thank ob and schematic for your support.. I am new at this and all the help i can get is appreciated. I switched the coils but the middle spark plug is still not firing. Then i switched the wires from the pack that goes to each coil primary like schematic said to do. I fired the motor and pulled the middle plug wire and it all most knocked me down from the shock. Does this mean that the pack is bad? Not even sure what a pack is.. lol ..

 

[petryshyn]

Re: 1979 mercury 70 hp

You have proven the coil to be good. The pack, or the trigger for the pack can be bad. Odds are the pack is bad, but we should check to be sure. The pack is the box that has the upside down Mercury tag on it in the picture below.<br />To check the trigger (which sits under the flywheel) <br />>return all wires to original position. <br />>Switch the wires as shown below and see if the spark returns to the center plug. <br />>If it does, it means the pack is good and the trigger is bad. <br />>If it still doesn't spark at the middle plug with the wires switched, the pack is bad....<br />

 

[thomas seale]

Re: 1979 mercury 70 hp

Schematic thanks for helping me... The spark returned to the center plug. So i guess the trigger assembly is bad if i understood you correctly.i really appreicate your help... thanks

 

[petryshyn]

Re: 1979 mercury 70 hp

Be careful when you make that assumption. The pack has a reputation of being intermittent. Reconnect all wires properly and see if spark is still missing from the middle cylinder. If it is, then you're sure....but if its back, its still possible its the pack....

 

[martinrobbins]

Re: 1979 mercury 70 hp

the images seem to be no longer avalible. i,m having the same problem.