Mercury 1972 thunderbolt misfire

[Iank]

Slight misfire on idle once throttle is held open it seems powerless and miss gets worse. Just bought this engine as a runner and clearly been bumped. Any help us much apperciated. Ian

 

[zaschf]

With the old mercs there is a problem with wire rot.
Can you check which cylinders are not firing. Faults with the ignition usually comes in pairs. With the Mercs the ignition system runs 1-2 and 3-4 as a pair.
Check your trigger module with close attention to the wiring.
Next in line is the switch module which controls the low/high voltage pulse to the coils and is triggered by, you guessed it, the trigger module.
I've recently rebuild a 1980 80hp Mercury and if you're keen to get it to go reliable, get yourself a manual. Well worth the investment.

Cheers,
Frits.

 

[Iank]

With the old mercs there is a problem with wire rot.
Can you check which cylinders are not firing. Faults with the ignition usually comes in pairs. With the Mercs the ignition system runs 1-2 and 3-4 as a pair.
Check your trigger module with close attention to the wiring.
Next in line is the switch module which controls the low/high voltage pulse to the coils and is triggered by, you guessed it, the trigger module.
I've recently rebuild a 1980 80hp Mercury and if you're keen to get it to go reliable, get yourself a manual. Well worth the investment.

Cheers,
Frits.

Thanks frits, i will remove that and give it a good once over and be back in touch.

cheers