Testing for spark

[cbfarmall]

I was working on a demo saw that I had flooded. Took the plug out, cranked it to blow out the fuel and then decided that it was a good time to check spark. Well, this saw being like an 050 Stihl means that you are limited where you can effectively ground plug. Ended up lighting half the saw on fire. Luckily only the fuel on the surface was burning and there was no scorching. Nobody was the wiser.

Now, I'm careful about how a ground a plug and where.

Chris B.

 

[ozflea]

I use an old car jumper lead to ground the plug to the saw that way the lead will reach anwhere on the saw for a ground.

Mc Bob.

 

[Al Smith]

The type I was refering to are induction spark testers.It picks up the spark pulse through the insulation of the wire.

 

[fubar2]

in the seventys i worked with a guy who did clean up in an all women assembly dept. in a factory. he said they had a gas powered sweeper you walk behind. all the women sat on metal stools. he said he wired em all together then to the plug wire while they were out to lunch. said they all rose up off the stools one right after the other down the line when he pulled the rope. wish id have thought of that.

 

[fubar2]

Oh and no its only generally good for one time per wife.

 

[2Coilinveins]

take out the spark plug, put the plug wire back on it, hand it to your wife, pull the rope. if she starts screaming youve got spark.

Hope you got a nice doghouse, Fubar, you must sleep in it alot with that trick!

I have a sparkplug that I've clipped the side electrode off of, and soldered a wire w/alligator clip to for a ground. Takes more energy to spark in a compressed air/fuel mixture than in plain air. Anything that'll jump a spark clear to the rim of that plug will fire in an engine.

 

[scottr]

Gap

2Coil , the B&S spark test tool is adjustable and is set to .166" to test for spark back when the L head engines had about 6 to 1 compression and fired a .030 plug gap . What is the gap of your modified plug spark test tool ?

 

[Lewis Brander]

Spark Testing:

I usually follow the old rule of thumb when checking for spark, which applies to older magneto setups. Most references to older magnetos state that if the mag will put out a spark to jump a 1/4" gap they are in good operating condition. I have a tester I made from an old wide gapped spark plug and have the gap set for .166". Usually if the spark will cross this gap the mag system should be fine. The old Disston I have wouldn't start and she wouldn't put out a spak to jump the .166" gap. Got a new coil and it will jump nearly a 1/2" gap. The saw has never failed to start since the coil replacement. I would be carefull with trying to test the electronic ignitions systems for fear of damaging the electronics with a gap that's too wide. It would be interesting to see if a scope could be used to acutlly see what the coils are putting out under compression pressures as far as voltages and measuring spark duration, but they would be expensive. They used to be a place in town where they could test varous magnetos and other igniton sysstems components, but have been out of business for years. There should be some simple affordable way to check out these saws to see what the system is acutally putting out under compression. But for now I just use my old trusty wide gapped spark plug. Take care. Lewis.

 

[scottr]

value

Lewis , a voltage divider and a peak hold type of voltmeter(if I remember correctly a Fluke 1210 ) or a storage oscilloscope would give a value . The 6:1 compression ratio engines used .166" spark gap test tools , does anyone know what the higher compression engines like the 8:1 compression ratio engines use for the spark gap test tool ?

 

[DanMan1]

If you insist on using the "jump the spark" method on solid state ignitions,you risk the chance of burning out the module,really.

That's an issue from early days solid state. I know a lot of people still preach this fear. If you have a healthy modern day ignition burn out from spark testing with an external plug, then send the junk ( saw and all) back where it came from. Any good ignition can withstand indefinite lack of current flow on the secondary side of the coil.

 

[Al Smith]

That's an issue from early days solid state. I know a lot of people still preach this fear. If you have a healthy modern day ignition burn out from spark testing with an external plug, then send the junk ( saw and all) back where it came from. Any good ignition can withstand indefinite lack of current flow on the secondary side of the coil.

Well I'm just repeating what I learned in a factory authorized school ,I attended from Briggs and Stratton.It's your coil,test it how you wish.

 

[ray benson]

I have a sparkplug that I've clipped the side electrode off of, and soldered a wire w/alligator clip to for a ground. Takes more energy to spark in a compressed air/fuel mixture than in plain air. Anything that'll jump a spark clear to the rim of that plug will fire in an engine.

Scott
This plug test setup is recommended by Homelite in their mid 1970's service manual. The gap is about 0.140". Seems to work .
Ray

 

[scottr]

.140"

Thanks Ray , I'm surprised that it is less than the B&S recomended test spark gap of .166" .

 

[2Coilinveins]

What is the gap of your modified plug spark test tool ?

0.1480"

Until Ray Benson's post, I didn't know that this practice was recommended by any engine manufacturer at any time. I'm no professional small engine mechanic; modified plug is just a trick that works well.

 

[scottr]

.148"

Thanks 2Coil .