1973 Mercury 50 HP 500 series serial # 3720337 NO SPARK. Please help!!!!

As stated in the title. 1973 Mercury 50 HP 500 series serial # 3720337 NO SPARK. Please help!!!!

The motor ran great all of last year but lost spark in the late Fall. Motor was stored inside over the Winter. Last week I pulled the motor from storage and checked spark and compression. Motor now had spark and 125 lbs compression straight across all 4 cylinders. I hooked up the gas tank and garden hose and ran it and it ran great. The weather did not cooperate until a couple of days ago. I fire the motor up in the driveway with the garden hose attached and ran it for a few minutes and then the motor stalled and would not restart. I checked spark and no spark problem has returned.

Can anyone give me some diagnostic help. I have lots of tools but no specialized marine diagnostic tools. I need help troubleshooting this ignition system.

Stator?

Trigger?

Brain Box?

Coil?

Re: 1973 Mercury 50 HP 500 series serial # 3720337 NO SPARK. Please help!!!!

I disconnected the Mercury switch (tilt switch) and turned motor over and had good spark for a few seconds and then lost spark again. I tested the Mercury switch and it is switching when turning the switch. I checked for spark directly from the Coil and I have a very dim spark with my spark tester. Where do I go from here?

Re: 1973 Mercury 50 HP 500 series serial # 3720337 NO SPARK. Please help!!!!

Heres a link to download a troubleshooting guide.
http://www.ebasicpower.com/downloads/cditech/CDI-Troubleshooting_Guide-MERCURY.pdf

Re: 1973 Mercury 50 HP 500 series serial # 3720337 NO SPARK. Please help!!!!

Thanks for the info. I will dive into it again. I have two different aftermarket service manuals but they don't go into any great detail.