High-tech Spark Tester

Lakesailor

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I've just made a spark tester to check the HT side of my Johnson outboard. According to the US forums I should get a clear bright blue spark across an air gap of 7/16". This is how someone suggested you could make one.

Any bets?

Sparktester.jpg
 

morgandlm

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I'm not clear how you then get this into the cylinder head ;-)

Seriously though I don't understand how this is better than simply testing with a spark plug unless you are simply proving that you can get a 7/16 inch spark in the open air.

Good fun though.
Morgan
 

VicS

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[ QUOTE ]
You know it has to be metric

[/ QUOTE ] Wrong its a Johnson engine. They are all imperial but what he hasn't realised is that the gap should be 7/16 of an <u>American</u> inch
 

VicS

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[ QUOTE ]
Could be shocking

[/ QUOTE ] You might be right. It is over 3 hours since his post. He is not normally quiet for that long! RIP
 

Heckler

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as a 14 year old experimenter, me and my mate discovered that his dads single cylinder petro cement mixer had a wonderful magneto on it, we experimented on how far awy from the plug we could take the lead before it stopped that wonderful chuff chuff chuff, we also discovered the joys of attaching earth worms to the lead and being fascinated on how its muscles contracted every time it sparked!!
 

andyball

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nothing wrong with that at all - you may miss the several KV up your arm of the traditional method though.


Are you still having problems , even with the factory-spec plugs?
 

Lakesailor

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The theory is that this avoids all the built in resistance of plugs and just tests the HT side of the motor. I shall also be wearing my latex mechanics gloves!

The motor does have an odd missfire. It runs nicely at tickover and starts no problem. It will accelerate quickly if you throw open the throttle, but if you ease the throttle forwards slowly it has a stuttering missfire and sometimes it clears, other times not. If I rev it in neutral by operating the carb linkages it doesn't rev cleanly, but that doesn't actually involve the timing advance mechanism linkage, so may not be a good indicator.
I am just setting about eliminating the HT coils, stator and power pack (I have some multimeter instructions to do that) and will do a compression test whilst I am at it.
If these all look OK I will clean the carbs, which many people think is the first place to look, but I will take the boat off the lake to do that in the garage.
I've spent many years listening to rough running engines and this one has an HT feel about it. It may be something as simple as the HT leads themselves, but I am ready to be suprised as I have a sneaky feeling the main jets may be gummed up a bit.

There ain't a whole lot to go wrong /forums/images/graemlins/blush.gif

Johnson1.jpg
 

andyball

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fwiw - all the "multimeter" tests in the world are pretty much useless on a cdi box that works. & even on most dead ones.
 

Billjratt

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The plug tester sold in car shops takes the form of a pair of plastic dividers with a guage calibrated in thous and a pair of studs halfway down each leg. that way, you can vary the gap and assess the strength of spark at each plug lead.
 

Lakesailor

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I only thought of that as I came across a page of instructions. My main object is to eliminate possible problem components.
It could well be the power pack, as beyond that everything is cylinder specific, coils, HT Plugs and carbs. My missfire is a bit more indistinct.
The other possibility is that it needs the carbs and timing "linking and synching" as the Yanks would have it.
But get the easy bits sorted first.
It's not unuseable, but I like things to be right.
 

Lakesailor

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I know what gap I need to achieve (in inches) and mine cost me, errm, nothing.
It's a bit of fun really. I like tinkering. /forums/images/graemlins/smile.gif
 

andyball

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the inductive pick-up timing lights can be a handy thing for this sorta prob.

Mine flashes only when a real spark occurs, and has been invaluable for isolating ign issues under load - even resorting to riding pillion with the thing connected, or taped to the bars. surprisingly easy to notice any misfires.
 

VicS

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This type of thing would be spot on but would need longer plug leads i think.

A Google search will locate other sources.

There is also a similar device available from Halfords with leads that should make it fit. Its a bit more expensive though.
 

William_H

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Just one thing might help Phil. Do the mixture adjust screws (if there is one) one the carbs have the usual correct effect. I am writing from experience of Johnson 6 with one carb 2 cyl. But I found the mixture adjust had no effect then found that the fine channel to the screw valve was blocked giving horrible effects like wouldn't power without a bit of choke.
I would suggest that the nature of the ignition system is such that it is either OK or dead with no poor performance. except possibly plugs.

One other check is to madly pump the fuel line bulb while running and getting the misfire. This will eliminate any fuel pump doubts or may fix the problem which will then point to a bad fuel pump. But then I am sure you are aware from years as a mechanic.
good luck olewill
 

Lakesailor

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Hi Will,
The idle is fine and as there are three carbs I'll leave the carb option till last. Another possible fuel issue (I think) is the possibility that the fuel solenoid (electric choke) is playing up.
Pumping the bulb has no effect and there is a low fuel flow alarm, assuming it works.
 
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