spark plug mystery 2 stroke 2 hp

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Graeme2004

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Joined
Jan 18, 2005
RO Number
16100
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106
2 stroke 2 hp outboard motor, ran fine then stopped, figured it was a gas starving issue. Took out spark plug and checked for spark, no spark. Holding spark plug I slipped off the edge of the engine and got spark! The spark is coming directly off the center of the plug nice and blue but when I hold the outer arm to the engine, no spark... any ideas what is going on and how do I rectify the situation... I tried 3 different plugs all with the same result, so it is not the plugs. I removed the rubber plug cap, bared the spark wire and wrapped it around the end of the plug old-school and it does the same thing... please help me get this thing running again!! Graeme
 
I can only guess the spark is weak. What kind of outboard? Does it have a magneto ignition, Coil, Points and Condenser? If it does,
1. Of course Coil could be weak
2. But if Condenser is leaking
3. Or Points are way off
4. Or Flywheel Key is missing/sheared...
...Then the spark could be weak. Might shock you but not be enough to jump gap or fire the cylinder.
 
I'm not getting a clear picture of your explanation of what's happening. You pull the plug and no spark...then you held the plug and slipped off the engine and got spark?? HUH?

Getting spark off the center of the plug??

The only part of the plug that needs to have spark is the center electrode and the ground electrode. Ground the threaded side of the metal casing against any part of the metal engine and look for spark between the center and ground electrodes. If you aren't getting spark from there, the ceramic insulator may be cracked where you can't see it and leaking spark straight to the metal casing.
 
Charlie hit it dead on.
To test his theory, hold the plug in your BARE HAND, and your thumb to the block.
If the Ceramic is leaking, you'll know right away.

I'll bet you've put two brand new plugs in the motor already. What'd you find?
 
The only 2 choices I can imagine are, either there was a secondary arc from the plug threaded area to a bare metal spot on the block if the plug was still close to the block,
or you were providing a personal path the neg ground for the ignition pulse through the plug .

If the latter, I'd expect you would have noticed that experience right off the bat & would have mentioned it .

Could you have been touching the plug ground strap to a painted or greasy area originally? No path to ground , no arc-spark.

You hadn't by any chance experienced a direct personal hit by a bolt of lightning, just prior to plug-testing, had you? Just wonderin'...
 
Thank you all so much for your ideas... when I hold the plug against block in normal check for spark fashion, no spark... when I hold the center pole close enough to the block a spark makes the leap from center pole to the block... My multimeter only goes to 5000 volts so I can't check to see what kind of voltage the points are throwing out to the plug, I tried several different plugs and reduced gap to 0.0000001 inch to see if that would get a spark... nothing... I am going to take the unit in somewhere to see if they can meter the output. Talk about frustrating... Graeme
 
some paint is a very good insulator. are you sure that you have good connections?
 
Most multimeters won't capture the quick spike of a single plug firing.
 
Sorry I didn't describe the 1st choice correctly. The arc should indeed come from the center electrode to the block if the threads or grounds strap was not touching bare conductive metal on the block.
Good to hear that is what was taking place, not somehow magically getting spark with the plug nowhere near the block or other ground.

The only other semi-reasonable possibility for a particular plug not visibly firing when you held it to the block would be if it had an internal grounding short between center electode and the ground electrode to bypass the intended gap, but I can't see that being the case with every plug you tried. Plus, the long arc to the block probably would have been from the ground strap or threads . .

Suggest you clip a ground jumper between the plug ground strap or threads and ,say, the neg ground bolt on the block if it is clean and bare, so as to rule out the paint insulation issue. You should see the plug spark then.
I imagine when you had the plug a little farther away from the block, the strong pulse was able to find a bare spot or crack in the paint to arc to.
 
Just to clarify, when you say 'center pole', do you mean where the plug wire connects to the spark plug?
 
Get a new plug and see what happens. I don't know how the starter is grounded but the engine isn't??
 
The plug is in the plug holder, so in the normal position as manufactured. I hold the curved part of the plug to bare metal on the block at opening of plug hole like I have done a thousand times before to check spark. No spark at all. I hold the plug off to the side of the plug hole and spark jumps from center pole of plug to the block - so juice is getting from the flywheel, through the plug boot, down the center of the plug to the block, but it will not do this in the normal way which is from the bent arm to the center pole when the outside of the plug is grounded to the block... it is the strangest thing... again thank you for all of your advice... Graeme
 
Did you try that in low light conditions so as to better see any normal spark? The longer arc to the block would be much easier to see.

Just for the heck of it you might check for continuity between the plug outer tip where the plug cable snaps on, and the threaded portion.
 
I suspect a break in the wire as there is spark in one position but not in another.
 
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