1976 merc 7.5 missfire

[capnfred]

I have an 76 merc 75 which has a missfire, if I pull the wire off the plug so it arcs to the plug it will smooth out, any ideas are appreciated. I have replaced the coils and the wires, and the plugs..... any ideas are appreciated... it starts easy, runs fine once I pull the plug wire..... thanks

Capnfred

 

[Laddies]

Re: 1976 merc 7.5 missfire

It sounds like low voltage at start up, needs to be tested with a DVA to be sure but that quite common as a switch box is a on it's way out

 

[capnfred]

Re: 1976 merc 7.5 missfire

Thanks, do you know what the voltage should be on the coils coming from the switchbox....I have quite a high potential on the secondary of the coil, will arc 1.5 inches or more.......also I have read many conflicting lists as for what the correct plug and gap should be. The previous owner had H10C champions in it.... any advice there is appreciated...

Thanks

Capnfred

 

[Laddies]

Re: 1976 merc 7.5 missfire

Switch box output should be 150+ volts with a DVA. L78V plugs some use L77J4Cs