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1987 75hp 4cyl switbox

R

raysmariner

New member
I have a 1987 75hp 4cyl mariner just replaced the switchbox and stator. #1 cylinder has spark but is sometimes weak. changed out plug wire plus swapped coils around and still has the same problem. Is there any thing else that may cause this problem
 
not sure how to check trigger. I took bracket from around flywheel the white wire coming from the trigger had corrosion so I cut it back to where it looked good and put new wire. still same problem going to replace the trigger just in case.
 
As I understand that trigger coil, a malfunction in one of the two circuits would effect two cylinders, not just one.

Jeff
 
How are you testing/checking to determine spark is weak? The trigger has no effect on spark output, it just tells scrs in box when to discharge capacitor. Spark output is is controlled by the stator,capacitor,coil, plug wire, plug and ground. The stator charges capacitor in switchbox and if other 3 are fine doubt its stator or box.
 
I used a spark gap tester #2,3,4 has strong constant spark but #1 fades in and out. changed out plug wire going to swap out coil again and look at all the grounds.
 
i have had a flaky trigger signal pick on one cylinder...weak signal and signal cutting out...but if the missing fire on two switchboxes on the same cylinder then i would not suspect trigger..but its possible...
 
tested trigger it was good so changed coils and redone grounds, finely got good spark on all cylinders. did a compression test got little over 150 psi on all cylinders, still runs ruff so now onto carbs.
 
A bad ground, eh? Something for all of us to keep in mind when troubleshooting.

That 150 is a good number.

Jeff
 
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