Topic: Can someone explain this spark check procedure better?

[elquenada]

i went local parts store for a spark checker an noone carries it.  Do i want to make my own like the one seen in this pic:

http://www.dansmc.com/sparkcheck.jpg

What I dont understand is what the clip is soldered there for because in this pic it does not look like its clamped to anything.  Can someone explain how I should or should not be using this thing before I light greasy engine on fire.  thanks

[Patrick]

To check your spark, pull the plug cap from a spark plug. Put a new spark plug in the cap. Ground the plug diode to a bolt on your engine. Push starter button. Look for spark. Repeat with the other wires. When the engine turns you should see a nice blue spark. If you don't then you have an issue.

Patrick

[BVCB650]

Looks like the clamp may be on a bolt head, but not sure. That would solve the grounding issue. Might make the plug spark easier to see, but to me, it's kind of like re-inventing the wheel. The old way was good enough.

[elquenada]

so just make sure the tip of the plug is touching a bolt and hit the starter?  thats pretty much what I was thinking.  thanks

[chickenman_26]

so just make sure the tip of the plug is touching a bolt and hit the starter?  thats pretty much what I was thinking.  thanks

If your ignition can cause a spark with the plug laid on the head, that's no guarantee it can fire the plug under compression. That tester isn't just a spark plug with a clamp on it. It's a special design plug shell with thin wall and no side electrode. The gap between the center electrode and the shell is 5mm, so it'll test the strength of your ignition by forcing it to develop enough voltage to fire across a much larger air gap. This simulates actual operation in the engine. It's a real handy tool, and not expensive. The top terminal can be screwed off for use with NGK type resistor plug caps.



http://www.tooltopia.com/index.asp?PageAction=VIEWPROD&ProdID=5490

Stu

[BVCB650]

What condition has to be present for a plug NOT to fire under compression?

[Don R]

Low voltage at the plug due to low battery, poor condition of coil, 12 volt or plug wires, too much fuel, burned points, oil or other contamination in the cylinder caused by worn rings or valve guides. etc.

[BVCB650]

I understand all that. What makes the plug not fire? What stops the spark? To me, a weak spark outside the chamber is a weak spark inside. A strong spark outside is strong inside.

[Patrick]

That's kinda the way I see it, BV. He's checking the spark. If he had asked about lack of combustion, that's a different answer.

Patrick

[chickenman_26]

I understand all that. What makes the plug not fire? What stops the spark? To me, a weak spark outside the chamber is a weak spark inside. A strong spark outside is strong inside.

The higher the compression and the weaker the fuel mixture, the more secondary voltage is required to ionize the plug gap. So the fact that a plug shows a spark in free air under no compression doesn't indicate it'll be fired reliably by the ignition system while the engine is running. All it basically tells you is that the coil wires aren't swapped and the points are working. Weak spark vs. good spark? If the coil can produce enough secondary voltage to ionize the plug gap, it'll produce a spark. But that doesn't take a heck of a lot with a .028" gap with no compression. When a bike idles well but misfires badly under acceleration, the problem could well be low voltage the ignition system, a weak coil, bad plug wire, excessive plug gap, etc. A spark tester will expose those problems, especially if it's adjustable (which the one pictured isn't). Just saying...

Stu

[elquenada]

great info as usual.

i tried doing it the old fashioned way and the spark seemed a little weak on all four cylinders.  i'll have to test coils and wires to see if ther up to spec.

[BVCB650]

great info as usual.

i tried doing it the old fashioned way and the spark seemed a little weak on all four cylinders.  i'll have to test coils and wires to see if ther up to spec.

How does one go about checking the coils to see if they are up to snuff?

[mystic_1]

Usually by measuring their primary and secondary resistance.

There are actual coil testers out there which will test the coil under load and tell you more about it's condition, but for a quick go/no-go test measure as per the workshop manual.

mystic_1