best way to see if a plug is firing.....

[nodoubt]

think i got 1 thats not sparking....any ideas....if its not....what would the problem be?? bad wire ?? powerpack....?? seems a little slow coming out of the hole and will not turn over 5000 rpms without backing off....thanks alot.....

[ReelWork]

Well, there's the obvious, have a young kid (either your own or neighbors) hold the plug and turn it over. If he jumps, it's getting the spark!

Actually, you can pull the plug and if you have a place where you can control the light, crank it and you should see the spark. If you can't see it due to obstruction, have some stand there or turn it over for you..

Make sure you have the fuel shut off...

[Sparks Signs]

you can get an inexpensive single plug spark tester form auto zone. I have one in my tool box and it works great

[jtburf]

a philips head screw driver and grounding it out between the spark wire end and the block while someone
turns over the motor!!!


john

[Sea_Dad]

you can also take the plug out and ground the electrode against some bare metal like a bolt head and then you can check the plug as well.

[Mist-Rest]

I was told that with the CDI box's on a lot of motors to BE SURE that spark is able to go somewhere. Just don't leave unused spark plug boots "hanging around". have them hooked up to something while testing.

[tidester]

Use a known good spark plug, and ground it to the engine with a jumper cable. That way, you can position it to see it spark, away from fuel. I've got a spark plug that I converted to a spark strength tool that way. I have a collar on it that I can use to position a ground electrode. There is no ground electrode on that old plug - just a pointy set screw and a viewing window. I've got some wire soldered to the shell, and a small clamp on the other end of the wire.

I've also got a spark tester (the type you lay against the spark plug wire lead and look at the neon tube), but it's too dim to see the strength of the spark. I prefer the plug method when appropriate.

[nodoubt]

thanks for the advice guys.....ill check it out next weekend when i get back to the lake...... .......btw....can just 1 single wire be replaced on a yamaha 250, 92 model if its bad.....do yall think it might be the power pack if its not getting fire ? is it common for 1 lead from the power pack to go bad......sure hope its a bad wire if im not getting fire..thanks again.....

Here's an easy way, most times it works to isolate which cylinder isn't firing. Start the engine and let it idle. If it's missing a cylinder, should be running a bit rough. While idling, remove a spark plug wire. Did the idle get rougher? If it did, that's not it. Keep doing it until you remove the wire that makes NO change in the idle. That'd be the one! Simple process of elimination.

[radioshop]

I prefer to take a test light and, pierce the spark wire jacket.

[BW23]

I used a timing light on my 225 EFI MERC to find a intermittent CDM(spark plug module). Nice thing about this approach is you can have a friend drive the boat and move from plug to plug.

[Mist-Rest]

Always have a friend pull the wires one at a time to find the dud.