1987 inline 115 cyl 3 and 4 spark intermittent.

[Waywardtravel]

I have a new to me distributorless merc 115 inline.

I just got it running but it is missing badly on cylinders 3 and 4. Its intermittent but seems to be good and planes perfectly when I tried.

I tried to link and sync and noticed the center carb a/f had zero change in RPM. A few minutes later it was firing on those cylinders. I may have changed RPM.

I understand that the swithboxes are 135 and 246.

I believe the stator leads only supply equal voltage to the top box for all 3 and bottom box for the other 3.

I have A spare parts engine to parts swap but I'm a bit confused. Trigger on both cylinders? Stator I don't get.

Carbs rebuilt, swapped number 2 carb to troubleshoot.

Then hooked up a timing light to number 3 then 4 and saw very intermittent spark. Maybe 1 in 6. I could get on it and it was great above plane?

Thanks for any help.

 

[Mybiggles]

Intermittent spark on my tower of power was the switch boxes. The cheap Chinese ones on eBay have worked fairly well for me so far.

That being said test the trigger, and move some coils around to see it the loss of spark stays in the same spot or moves with the coils

 

[Waywardtravel]

Thanks,
. I swapped switch boxes, coils, and mercury switch from a parts engine engine or two of those things fixed it.