TOPIC: switch box or stator ?

Buddy of mine brought his fathers bass boat with a mid 80s brown stripe Merc 115 over today , starts runs good on several cylinders but not all ,sounds like 3 and every so often it "kicks" the missing cylinders in and hits on all 6 . # 3 has a real hot spark 1-5 ( cant get my big paw down in there to pull # 6 to see if its firing )dont seam as strong ... cant isolate it to any particularcylinder being dead ... ran out of light so called it a day ,any ideas ? thanks

compression chek first.

My first thought - based on your description - is to ask if perhaps you might still have last year's gas in your tank.
I had one acting like that here this last weekend.
It was running with an intermittent mis-firing going on.
I found (2) somewhat fouled sparkplugs and when I asked about the gas he confessed that it was last year's fuel mix.
I let him use my portable tank and swapped out the (2) sparkplugs.
It started good and ran good during the subsequent lake test.
I encouraged him to return with the motor when we both have time so I can open the carburetors up and make sure no water or nasty old fuel mix was still down in the bottom of the bowl chambers - where simply opening the main jet plug won't drain it off and it can continue to cause grief for quite a while.
The ethynol gas of today doesn't have a very long 'shelf life'.

That being said,...Be really careful handling those sparkplug leads - there is enough spark there to drop you in your tracks. Seriously.

Disconnect the fuel supply and wipe any fuel spills out of the lower pan before proceeding with the following testing.

Pull all the sparkplugs, push them back onto their leads, ground every sparkplug to the powerhead to control the spark output or you could damage the ignition components.
Then have someone spin the motor via the control box ignition so you can watch and see if you can see spark on all (6) under these controlled circumstances.
If all (6) have spark, take (1) old sparkplug of the center gap design, and spread the gap to 1/4"+. Use this sparkplug to test each sparkplug wire's output.
This style ignition should jump 3/8" so you'll need to watch the length of the sparkplug wire being tested to insure nowhere along the lead is it close to engine ground as you want the spark to jump at the center gap of the test plug only.
If you find that one or more of the sparkplug leads will NOT jump the 1/4", you are well on your way to identifying which cylinder's ignition is having issues.
If all (6) jump 1/4"+ try and set up a way to test for a controlled arc of about 3/8".

Report your findings and we'll proceed with how to test the specific components.
If you have a DVA meter - it will be helpful.
If not - I can probably explain some back yard techniques to chase down the intermittent failures - the most fun kind of failures to troubleshoot.


I have attached a picture of the tool I made to control spark during testing, etc. It is a piece of steel flat bar with (6) old center gap style sparkplugs welded to it. The gap of the sparkplugs are spread to about 1/4". Simply clamp one end of the flatbar to a good powerhead ground and plug on all the sparkplug wires.
I recently bolted a ground strap onto one end of the flat bar so I could clamp to a powerhead ground easier.
Thom

Only had a hour before dark to look this thing over ,Im suspicous of the fuel to as I think hes a Im done with it so park it kind of guy ... all had time for last night was get a battery to it and get it started to hear it (his battery is junk) , while running it would try and fire the other cylinder(s)occasionaly squirted gas into the carbs just to be sure it wasnt a nofuel problem ... did appear to be a weak spark issue .. if its not raining tonight will poke at it some more and report back ...

made a tester up like the one in the picture , have spark on 1,4&6 , 2,3&5 are dead .. it acted like it was running on 3 cylinders with one or two others kicking in occasionaly .. longer it ran the less frequent they would fire .. the ones with spark have a good spark !

correction to my last post tested again this morning before sun came up and I have spark on 1,2,4 and 6 3 & 5 are dead !

tonight I robbed a coil pack from another motor and jury rigged a pair of coils , now have spark on all but # 5 , tried a different plug and coil and still no spark ...

now that you have spark on both sides and isolated to #5

Now check the continuity of #5 wire and at the cap #5 contact points

if you cleaned the contacts points in the cap already its most likely the plug wire

this is a 85 motor uses 2 switch boxes , have continuity back to the switch box and swapping the green hot leads moves it to another coil ... thinking switch box ?