mercury 90 3 cyclinder

[BOAT DOCTOR]

Rebuilt motor.Ran it today on hose just checking it out sounds good revs up the rpms.But when i do a cyclinder drop test to check fire and see if it is hitting on all cyclinders and i pull the #1 spark plug cap off i cant see the fire and the cyclinder doesn't drop.Took off spark plug boot and held the end of the spark plug wire to plug i can see the fire but it looks weak.rebuilt carbs,fuel pump,and has fresh fuel.Not sure what could cause just the #1 spark wire to send a weak spark.Other two plug wires i can pull them off and it drops off good if i take off two spark plugs caps off while motor is running and take the #1 spark plug and touch it to the plug you can barely hear it hit but it hits.any clues to point me in direction.kind of lost but wont give up.THANKS

 

[87TrackerOwner]

Re: mercury 90 3 cyclinder

If this outboard has a coil for each cylinder, you could try swapping them around to see if the problem follows a coil. When I was younger, we had a 40hp Merc which would burn up a coil every year or two. My dad fought it and had it repaired several times.

I have an 80hp 3cyl with a deteriorating trigger wire which makes me nervous about looming electrical issues.

 

[jeffersondodson561]

Re: mercury 90 3 cyclinder

Did you bore/hone cylinders, were your cylinder taper in spec. was your ring end gap in spec at all positions in the cylinder? If you think your coil is suspect, check primary and secondary resistance, high tension lead resistance, or swap plugs to see if problem follows plug...

 

[BOAT DOCTOR]

Re: mercury 90 3 cyclinder

yes bored out to 030 compression is 135 on all three cylinders.air fuel misture screw is set at about 1 and quarter turns out sync and link carbs.going to go check timing and coil right now brand new plugs