40HP Merc 402 1974

rudy0159

Recruit
Joined
Sep 29, 2004
Messages
2
Ok, I need some help please. I was on the lake last week and all of a sudden one of the cylinders stoped firing, when I got home to trouble shoot the other cylinder stoped firing. I have replaced one of the ignition coils. and the other one is on the way, the cylinder with the new coil is still not firing. The Stator was replaced this past winter. Does any one have any sugestions? I was told by one person that is could be ignition trigger. is that correct, I want to get this fixed as soon as possible with as little money as possable. Thanks
 

andrewkafp

Lieutenant Commander
Joined
Mar 15, 2003
Messages
1,668
Re: 40HP Merc 402 1974

That's a 2 cylinder motor.I would firstly do a compression test to confirm you have compression in both, then check the wires leading from the trigger to the switchbox for breakage or corrosion, You will need to remove the insulation from the loom. Corrosion in these wires is common for that era of Mercs. If you dont want to remove the loom insulation to expose the different coloured wires, just use a probe type tester from switchbox end to trigger end, to show continuity.
 

rudy0159

Recruit
Joined
Sep 29, 2004
Messages
2
Re: 40HP Merc 402 1974

I have done a compression test, both cylinders are good, I know some of the wires going to the switch box are brittle, however the two wires going to the trigger are brand new.
 

andrewkafp

Lieutenant Commander
Joined
Mar 15, 2003
Messages
1,668
Re: 40HP Merc 402 1974

Also check the green thicker wires from switchbox to coils.It is not uncommon for the switchbox to fail (Won't wish that on you though).The only real way to test that component is to try another one on the motor.
 
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