Need help understanding the operation of my 1978 Mercury 115hp inline 6

[Cheeseman]

New to the forum. Thank you.
I have a 1978 mercury 115hp inline 6 2 stroke outboard. Getting strong spark on cylinders 3 and 6, very weak but noticeable on the remaining 4 cylinders.
I has led me to believe that the rotor/rotor shaft may be bent....... Put on New cap, wires and plugs. Came with new CDI switch box.
Until I read that some mercury only fire on 2 cylinders at low RPM and then kick in as the rpms rise. IS that true for my model?
Your advice will be most appreciated.

 

[faztbullet]

Not your model. If it fire all will fire, check plug boot as spring rot off inside and cause weak spark

 

[Cheeseman]

Not your model. If it fire all will fire, check plug boot as spring rot off inside and cause weak spark

Thanks for the response. I have put new wires , plugs and cap on it. No change. I used the number 3 plug wire (known good) and went around the cap trying each cylinder, still again no change, 3 and 6 strong spark weak spark on all the others.
Any other suggestions you might have?

 

[fastjeff]

Bad switch boxes?

I suggest you use a DVA meter to find out what's happening. I bought an attachment for my ohm meter on Amazon that cost about 30 bucks.


Jeff

 

[Cheeseman]

Switch box was replaced with a CDI unit part# 114-2986 w/coil. Have great pulsing spark straight out of the coil. Great spark on 3 and 6, weak spark on the other 4
Can pictures be added to the thread?

 

[faztbullet]

Bad switch boxes?

Where is a cap and rotor used on a ADI ignition??? Check the carbon pile and spring in bottom of cap that contacts rotor.