1987 Mercury 35hp Issues - Help!

[JayRd7]

Hi everyone,

For a while now I've been experiencing issues with my 1987 Mercury outboard. It's a 35hp, electric start. Here's the problem. 9 out of 10 times when I take the boat out, the motor will start up and will only be running on 1 cylinder. After about 15-20 minutes, the 2nd cylinder will randomly kick in and I'll have full power. Sometimes the cylinder will be fine and stay running until I'm done, however sometimes it kicks in and out, and im constantly losing/gaining power. I've changed spark plugs of course, as well as connecting wires from the spark plug to the distributor. Could it have something to do with the power packs that control the cylinders, or could it be something really obvious that I'm not getting here. Any ideas would be appreciated, thanks so much,

Jared

 

[WillyBWright]

Re: 1987 Mercury 35hp Issues - Help!

There are four basic components to the ignition system. The stator that produces the electricity, the trigger that tells the switchbox when and where to spark, the switchbox, and the coils. Oh yeah, and the sparkplugs.

The stator could be putting out less than adequate power, but that usually leads to misfiring on all cylinders.

One trigger feeds two cylinders. So if either or both are firing, it can't be the trigger.

Switchbox failures are common and unpredictable.

Coils can also fail, but are among the most reliable parts along with the trigger.

You can usually tell which cylinder is firing more by the sparkplug deposits. Ideal deposits are dark brown, slightly damp-looking. Clean plugs usually point to the problem cylinder.

You can test for misfire while running with a timing light. If it flashes, it's sparking. I tape the trigger on and place it in an easy to see area, then take successive runs trying different cylinders and watch the flash.

You can see if a coil is the problem by swapping coils. If the problem travels with the coil, replace the coil.

 

[JayRd7]

Re: 1987 Mercury 35hp Issues - Help!

Thanks for your help, I'm almost certain at this point it's the switchbox, it makes the most sense. If it's faulty then that would explain why that other cylinder randomly kicks in and out. Is there any way to test the box to see if that's the problem, or should I just risk it and order a new one and see if that was indeed the problem. Thanks,

Jared