engine stopped no spark

[fluidjuice]

I have a mercury 1991 40 hp classic
my problem is the engine has been running fine all season, swapped it to my new second hand fishing boat and started it first time on muffs.
went to test it in the water and flattened the battery trying to start it , So i checked spark and found no spark.
Took it home checked the 20 amp fuse and unplugged engine plug sprayed some wd-40 in it and plugged it in again and engine started fine on muffs.
So today i took it to the water again and the engine started and ran fine untill i got out of the harbour , i got upto about half throttle and it just cut out like turning off the key.
Managed to get towed in by a very kind fisherman , got it home , tested for spark and NO SPARK again, any Ideas anyone? just seems funny that it is so intermittant
Thanks Fluidjuice

 

[Laddies]

Re: engine stopped no spark

Go to the switch box and disconnect the black/yellow wire it's the kill wire to the key switch and see if it runs then, that will tell you if the system has a shot in it or if you need to test the system. If you need the test let us know and we can help. remember the key will not shut the engine off without touching the black/yellow on the box terminal.

 

[fluidjuice]

Re: engine stopped no spark

Yep dissconnected black/ yellow wire and engine fired. so where do i go now, as i have replaced wire back on terminal and engine started up on muffs but my worry is that it will stop again when out at sea so what needs to be done to test for definate

 

[Laddies]

Re: engine stopped no spark

You need to do the test while the engine is acting up or you don't prove any thing, if the engine didn't run and you disconnected the wire then you have a short in the harness or bad switch.

 

[fluidjuice]

Re: engine stopped no spark

thanks laddies but what switch do you mean as i dont have a kill switch fitted, do you mean ignition switch or mercury switch,could someone please explain the function of the mercury switch please.

 

[fluidjuice]

Re: engine stopped no spark

Just an observation which might/might not be a problem????
on checking my dash mounted ignition key switch i found two black/yellow wires both connected to terminals on back of switch, one of which runs into engine wire loom and off to the engine, the other one is just about 8 inches long and the end taped up , as i have no kill switch fitted i presume this wire is redundant,upon closer inspection i noticed the ends of the taped wire were exposed and had been touching the (metal)steering wheel hub.my question is would this ground out the kill curcuit and prevent the engine from sparking, as my problem is intermittant and wondered if this wire was moving about and only touching hub sometimes,
I may be barking up the wrong tree completely but i just thought any info could help build a bigger picture to help isolate my problem.
also as stated before at this moment the engine is starting so would i have to be worrying about tilt switch etc.

 

[Laddies]

Re: engine stopped no spark

If the black/yellow under the dash was touching the steering system yes it would ground the engine ign. out