What Do the Plugs Say?

[minuteman62-64]

Now that I've got (at least for now) the cooling issues resolved with my '82 Mariner I'm looking at another issue.

Motor is 30HP Mariner 30A, CD ignition, 2 cylinder, single carb and relatively new (about 30 hours) plugs. No. 1 (upper) cylinder plug seems to look like it should (light tan deposits on insulator). No. 2 (lower) cylinder plug has black deposits on insulator.

Based on my reading, #2 cylinder is running rich - maybe weak spark from bad coil winding. Is this correct?

How do I test? My shop manual has test procedures but they are based on a "Mercury Ignition Tester" which I don't have. I do have one of those gap type spark testers and a volt/ohm meter.

Replacement coils for this motor are kind of expensive ($256 for OEM) so I don't want to just go buy one on the chance that it will fix things. Or, is it a big enough problem to worry about? The motor in present condition produces plenty of power for my style of boating.

See photos. #1 is top cylinder and #2 is bottom cylinder.

 

[Chris1956]

If it runs OK, run it. I doubt spark is weak. You can check to see that it "snaps" with a blue color. If so, it is fine.

 

[Sylva-Ranger]

If you suspect one coil , may be just put the no 1 in place of the no 2 and recheck the colours after running.

I don't think this is an ignition problem…...

 

[flyingscott]

Is your motor doing a lot of idling/trolling

 

[minuteman62-64]

If you suspect one coil , may be just put the no 1 in place of the no 2 and recheck the colours after running.

I don't think this is an ignition problem…...

Won't this mess up the timing? Have the plugs firing at the wrong time?

BTW, only one coil - so must have two secondary windings.

 

[minuteman62-64]

Is your motor doing a lot of idling/trolling

Yes, in fact I run it in a barrel more than I run it on the open water. Maybe I just need to use it more

 

[minuteman62-64]

Don't know if it is relevant, but, compression about a week ago: #1-136; #2-135. Both measured cold.

Appreciate the responses. I'll try observing the spark as soon as I educate myself on how to do it w/o screwing up the coil.

Maybe I just need to use it more.

 

[jimmbo]

Yes, in fact I run it in a barrel more than I run it on the open water. Maybe I just need to use it more

It was designed to run on a Lake, River, or Ocean while clamped to a boat...

 

[Sylva-Ranger]

Won't this mess up the timing? Have the plugs firing at the wrong time?

BTW, only one coil - so must have two secondary windings.

Like many CDI 2 cylinder (outboard, snowmobiles etc) whit only one double coil , the 2 plug fire at the same time every 1/2 turn...If you invert the 2 hi tenson wires that change nothing on the timing or anithing else.

On this type of double coil, usualy the sparks of one side is a little bit stronger than the other side…….Not enough to see a difference in a good shape ignition system, but whit a bad primary (EX: stator) that sometimes make a difference.

 

[minuteman62-64]

It was designed to run on a Lake, River, or Ocean while clamped to a boat...

Come to think of it, that's why I bought it. However, old age is taking it's toll and it is more and more work just to hook it up, tow to Bay, launch/retrieve and bring home.

 

[jimmbo]

I guess running it a barrel, sitting in a chair, with your eyes closed, listening to the sounds, inhaling the sweet smell of burnt 2 stoke oil isn't too far off of being there. Cheaper too, a bit of a breeze and a few drops of water from a distant lawn sprinkler and it is just about perfect

I know to imitate mine, I stand in a Cold Shower and Shred a couple of 100 Dollar bills, equal to a day at the lake, without the hassle

 

[minuteman62-64]

Like many CDI 2 cylinder (outboard, snowmobiles etc) whit only one double coil , the 2 plug fire at the same time every 1/2 turn...If you invert the 2 hi tenson wires that change nothing on the timing or anithing else.

On this type of double coil, usualy the sparks of one side is a little bit stronger than the other side…….Not enough to see a difference in a good shape ignition system, but whit a bad primary (EX: stator) that sometimes make a difference.

I did not know that. So, the plug on one cylinder fires when the piston is near TDC and, at the same time, the other one fires with the piston is about all the way down?

 

[Sylva-Ranger]

I did not know that. So, the plug on one cylinder fires when the piston is near TDC and, at the same time, the other one fires with the piston is about all the way down?

On 2 stokes yes , on 4 strokes the other piston fire in "chevauchement" in french.....................Sorry don't know the English word for describe when the piston is in TDC and boths valves are slyghtly open (end of the exhaust stroke and begining of the intake stroke).

Is the same on Briggs & Stratton 4 strokes engine that have the fire on the crankshaft (flywheel) and fire every revolution, and the power stroke is every 2 revolution.

 

[jimmbo]

I did not know that. So, the plug on one cylinder fires when the piston is near TDC and, at the same time, the other one fires with the piston is about all the way down?

If you mean the plug firing twice per revolution, once a near TDC and again near BDC, then no. On a 2 stroke that could ignite the air-fuel mixture transferring from the crankcase, and with the intake ports open the combustion would flow into the crankcase. a 2 stroke would not be able to run
On a 4 stroke, it has been done, with the spark happening every time the piston approaches TDC, as half the time the this would be during the exhaust stroke , prior to the intake stroke. However, on an engine with wild valve timing, a similar situation could occur as the intake valve is opening prior to the piston reaching TDC on the exhaust stroke, and combustion could occur in the intake runners

 

[minuteman62-64]

Now I'm getting confused. My '82 Mariner is, of course, a 2 stroke. I was commenting on the statement that: "

Like many CDI 2 cylinder (outboard, snowmobiles etc) whit only one double coil , the 2 plug fire at the same time every 1/2 turn...If you invert the 2 hi tenson wires that change nothing on the timing or anithing else."​

If the plugs both fire every 1/2 turn won't they both be firing when one piston is near the top and one near the bottom of their travel?​

 

[flyingscott]

On a 4 strk there is an ignition called a wasted spark it fires both plugs at the same time. It can be done because of the 2 extra strks and the valves. On a 2 strk that cant't be done because of the ports design. Since it has open ports if you fire the plug at the bottom of the strk you run the risk of backfires through the motor. So no those coil assemblies usually are 2 coils mounted into one assembly.

 

[Texasmark]

Looks to me like it's past time to have new plugs and most Merc service manuals I have had list NGK plugs. Change the plugs to the correct NGK and THEN start "pulling your hair out" on a problem that may have just been solved. Grin

 

[minuteman62-64]

Looks to me like it's past time to have new plugs and most Merc service manuals I have had list NGK plugs. Change the plugs to the correct NGK and THEN start "pulling your hair out" on a problem that may have just been solved. Grin

Existing plugs are the NGK's specified in the manual w/about 30 hrs. Based on the responses to date, appears I should take it for a good run on the water before worrying too much (and pulling out my hair ) about plug appearance.

Since I have a spark gap tester I think I will check on the spark from each cylinder. I see a number of references to 7/16" gap on the tester - is that the best setting for the test?

 

[Sylva-Ranger]

On a 4 strk there is an ignition called a wasted spark it fires both plugs at the same time. It can be done because of the 2 extra strks and the valves. On a 2 strk that cant't be done because of the ports design. Since it has open ports if you fire the plug at the bottom of the strk you run the risk of backfires through the motor. So no those coil assemblies usually are 2 coils mounted into one assembly.

Now i"m confused ….Why the ignition can run on some 2 strokes outboard engine (usualy some Japanese engine like some Suzuki and older Mariner and Spririt) whit only one (double) coil and only one positive primary wire ?

And why can we reverse the sparp-plugs wires on a 2 cyl 2 strokes snowmobile (95% of them have only one coil whit one positive primary for the 2 cylinder) and the engine still running perfecly ? why this can happen if they don't fire at the same time ?

 

[minuteman62-64]

Now i"m confused ….Why the ignition can run on some 2 strokes outboard engine (usualy some Japanese engine like some Suzuki and older Mariner and Spririt) whit only one (double) coil and only one positive primary wire ?

And why can we reverse the sparp-plugs wires on a 2 cyl 2 strokes snowmobile (95% of them have only one coil whit one positive primary for the 2 cylinder) and the engine still running perfecly ? why this can happen if they don't fire at the same time ?

I took a look at the ignition circuit schematic (which I should have done in the beginning). See attached. One coil with one primary and one secondary winding feeding two plugs. Looks like it has to fire both plugs with one near TDC and one near bottom.

Based on the diagram, doesn't seem to be any reason why one plug would have a different spark than the other (unless plug wire had different resistance) and why I couldn't switch the plug wires. .