I think I got My Motot Fixed -- And Then

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After months of guessing and replacing parts and guessing and cursing - Finally discovered one of the cylinders on my 8hp evinrude was not firing all the time.   Replaced the coils awhile ago so that leaves the power pack.  The install was easy and I tested the spark on both cylinders and I just Know I saw spark on both.

Well we were filming the install and of course the spark test -- last night I was processing the film and you know I can't see the spark on one of the cylinders-------- Arrrrrrgggggh

Won't be able to sail this weekend because TS Bonnie will stir things up too much  --  The suspense !!  the Drama !!  How bad do you suppose the shock would be if I try another test in the rain???   HHHOw many volts is that?  MMaatttt

[Salty19]

Matt-

The volts to the plug wire is very high.  Could be anywhere from 10K to 40K volts with very low amperage.  The coil is what raises the voltage so high.  It's probably 14-19 volts on the stator side of the coil.

You won't kill yourself as it's low amps but touching the spark lead with the engine turned over will definitely zap you enough to not do it again! Instead, tape the spark plug with lead attached to the cylinder wall for checking spark.

What about the spark plug leads themselves and leads from the power back (ie stator) to the coil?  These tend to wear with age even if they are never moved.  Corrosion from the air and decomposition from heat. Stretching of the lead which fits over the end of spark plug can cause this too.

The coil is probably OK but check for TWO coils on your twin cylinder. Some motors have them, others they combine both coils in one solid state unit.   Then again if the voltage on the stator side is good and the plugs still misfire, it could well be the coil or the leads to the coil.  Another thing to check is the leads coming out of the stator to the coil.  If you do have two coils there are two leads.  Whichever one is not firing, check continuity and resistance.  There should be little resistance (perhaps 3 Ohms or less) here.  I presume you have a volt/ohm meter.

Also something small to check but it's important.  Spark plug gap.  Don't guess or install plugs without checking and adjusting the gap. Increased gaps need larger voltages to fire. The the voltage is not available, it won't fire but the next spark event it might. This tends to overheat coils as it has to store it in a capacitor that's probably not made to store it for very long (a small fraction of a second). 

if you have repeatedly pulled the starter cord with the ignition on (coil cord attached) and without the spark plugs installed, you may have fried the coils as they were not able to release the energy they generated. they are not designed to store energy for long (again fractions of a second then release it all).

Good luck, hope you can find the culprit!

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Salty

Thanks for the advice.  So far the weather hasn't cooperated for an on the water test - maybe next weekend.   Hope you are wrong about the last point - gulp!  Matt