Maddening intermittent no spark issue...Thanks to all who have helped me so far...

[Luckymann77]

As the heading says...
1977 Mercury 1150 I6 serial # 4735111
Distributor ignition...
Newer battery fully charged.
Did the "jumper test" across switchbox per CDI website.
Suddenly got spark.
Then...
Ignition switch tested bad...replaced it.
New NGK buhw plugs.
Still intermittent spark.
Jumper test again...
Engine fired and ran for 30 seconds...
Then no fire...
jumper test again.
Sparked and ran all day.
Fired up each and every time...started and ran great more than ten times that day.
Several days later,
No spark again.
Did jumper test again...
Fired and ran all day again.
Replaced the switch box...
Fired and ran all day...great !!!
today...no spark again.
jumper test again.
Started and ran...till I got to the lake.
NO spark again.
Did jumper test again at lake...ran all day...great !!!
So,
what's the deal ???
I do unhook the battery when I get home after each outing...
Always negative on last and off first...
Scratching the noodle here...

 

[Chris1956]

I am not sure what the "Jumper test" is. Can you describe it?

BTW - Triggers can be intermittent, but I recommend you make sure the rest of the ign system works, before replacing it.

 

[Luckymann77]

Thanks Chris,
The jumper test is on CDI's website...here...page 66

http://issuu.com/cdielectronics/docs/cdi_troubleshooting_guide_-_2012_1?e=2044661/2001100

You unhook all the trigger leads from the switch box and place a jumper between the white and brown pole on the switchbox then install a wire on the black post long enough that you can "tap" it to ground...
Also saw cturboaddict do this on youtube...

This seems to "fix" the problem each time...so far.

Hate to hear that a trigger can go intermittent...
I have a replacement coil that I got off eBay...not proven that it works but will switch it out since I have it.

Was hoping that the trigger wasn't the culprit...very expensive.
Don't know where to get one on the cheap.

Luckymann77

 

[Faztbullet]

Trigger is bad......replace it.