1976 456hh 45 hp.magneto model

[Chrisham]

The top plug quit firing after about 1 hour run time.I replaced both plugs with new ones and it happened again.I installed one of the used ones that I had cleaned,while on the water ,top cylinder again.The plug looked good both times what would cause this.Motor has set up for years .My dad bought it new in 1976

 

[Nordin]

Does it foul the plug and destroy it?
Or is it the ignition coil that fail after about 1 hour?
Do running at low RPMs (trolling) all the time or do you throttle it up and running at higher RPMs?
Fouling plugs and make the plug to get shorted is due to the air/fuel mixture is to rich.

 

[Chrisham]

I mostly run at full throttle.I assume it's fouling the plug although they don't look fouled..I'm running 92 octane no ethanol 50 to 1.Plug runs fine after cleaning .Gas is fresh also.Coils are on the outside of motor .Would this be a magneto model.It has no cdi box

 

[Chrisham]

I assume coil is good if you change top plug it's an instant fix

 

[racerone]

Post actual compression numbers.----Have you checked fuel pump diaphragm ?----And does spark jump a gap of 3/8" on both leads?

 

[Nordin]

If you have the coils mounted at the block and there is no CD box you have a battery ignition system.
The ignition system need a 12V battery to work.
Check the coils for cracks, it is a common issue with this battery system.
If you leave the keyswitch in RUN position when you do not run the engine at least one of the coils will draw current because the points is closed and the primery winding in the coil will have the circuit closed.
The coil will heat up and crack the insulation.
The coils for battery system are not made for constant current through the winding.

 

[Chrisham]

If you have the coils mounted at the block and there is no CD box you have a battery ignition system.
The ignition system need a 12V battery to work.
Check the coils for cracks, it is a common issue with this battery system.
If you leave the keyswitch in RUN position when you do not run the engine at least one of the coils will draw current because the points is closed and the primery winding in the coil will have the circuit closed.
The coil will heat up and crack the insulation.
The coils for battery system are not made for constant current through the winding.

There are cracks on the coils

 

[Chrisham]

There are cracks on the coils.will this cause the spark plug issue

 

[Nordin]

Yes I assume that, the coils are affected.
When the coils are cold the insulation can be good, when they get warm the insulation can be bad and the windings maybe shorted.
A crack in the coil is not a normal situation.

 

[Chrisham]

Yes I assume that, the coils are affected.
When the coils are cold the insulation can be good, when they get warm the insulation can be bad and the windings maybe shorted.
A crack in the coil is not a normal situation.

Will changing the plug correct this .As soon as I change the plug it runs on both cylinders.i changed it on the water the other night and it corrected it

 

[Chrisham]

Post actual compression numbers.----Have you checked fuel pump diaphragm ?----And does spark jump a gap of 3/8" on both leads?

I checked the compression.I warmed it up idling it.The compression is 110 on both cylinders.I will have to get some help to check the spark

 

[Chrisham]

I checked the compression.I warmed it up idling it.The compression is 110 on both cylinders.I will have to get some help to check the spark

I have 2 coils ordered they were paid for on Oct 10.I don't think they are even shipped yet

 

[Nordin]

When it stop next time check for spark as soon as possible.
Are the plugs that you change out bad and not usable any more or can you use them again when they have cool down?

 

[Chrisham]

I clean them and reuse them.I keep some extra in all my boats.They are reuseable

 

[Nordin]

As I said before check for spark as soon as possible when it fail.
If you can reuse the plugs there are no rich mixture issue.
I think the coils are the culprit.