Spark tester

This is a general question regarding a specific application. My friend's 51 B with a distributor won't start. I didn't have any tools with me, but had an in-line spark tester in my pocket. Harbor Freight brand. It flashed when the engine was turned over, but sort of a dim orange. Is this by itself diagnostic of weak plug voltage or a marginal plug? Just wondering-most things in the world cause me to wonder. Thanks!

I never have used a spark tester and never will. I just pull the plug wire off and stick something in to sort of replace the plug and then hold it about a 1/4 inch from the block and spin it over. A good spark will be blue/white and jump a 1/4 inch gap or more. Or you can use an old plug and gap it as wide as you can and hold it to the block and spin it over and watch the spark

when I worked at the JD dealer here years ago an older gentleman came in to pick up his JD b hooked to a NH baler we worked o. The B didn't start right off so he held one wire in his had and told me to roll it over. Said he didn't think the spark was quite as hot as it should be. I don't recommend that method

Sounds sort of like how I showed the son about mags and why one does not want to hold onto a plug wire when you spin it over. I had just gotten a rebuilt mag for my 1935 JD-B and wanted to test it so I told him hold this and flipped it past the impulse and he jumped LOL

My Dad was never one to let discomfort stand in the way of work. He'd hold the plug wire in one hand, wet the fingers of the other and lay them on bare steel and have me roll it over. If the mag was OK he sure get a jolt. His motto seemed to be, "It's just pain, it won't hurt you".

I've used a spark tester like you describe, but only for proof of spark and not strength. If you want to test the strength of the spark you need to check it against ground through the plug first, you're looking for a good blue spark. Yellow is weak. If it is weak, then you need to check if it will arc from the wire to the plug, should be able to jump a 1/4" at least.

Lots of people are nervous about doing this out of fear of getting an electrical shock. I'm one of them, but you won't if you're careful. Just make sure you are insulated, rubber coated handles on the plier holding the wire or rubber gloves if you prefer.

"[b:654c4848f0][i:654c4848f0]I've used a spark tester like you describe, but only for proof of spark and not strength.[/i:654c4848f0][/b:654c4848f0]"

Same here.

Seeing the comments on the spark tester processes described below reminds me of an incident where I worked on an IH magneto from an F 12. I re-charged the magnet & installed new points. Cleaned everything & reassembled with a new cap brushes. It was one that had the settable impulse so if turned off it could easily be turned by hand without the impulse. When I took it back to him I had an old Champion D23 plug connected to it with a piece of bare wire daisy chained through all of the holes in the distributor cap to the plug with a 3-16" gap. This way the one plug received all the sparks. I wanted to show him that it indeed made a very nice blue spark easily jumping that gap. He insisted on holding it still on the work bench but I did not notice he had one finger touching that bare daisy chained wire as it came out of one of the bottom towers.

I deliberately rotated it slowly because I wanted him to see how well it sparked. I was so disappointed when it didn't spark I spun it faster for the next one. Still no spark. Then faster. Then I set the impulse & once more it did not spark!

Very embarrassed I began to apologize and tell him I'd take it back home to see what I'd done wrong. He with his very calm 90+ year old voice told me oh it works just fine! It gave me 4 very good sparks and I have no doubt it will start right up! I've had enough proof already!

Later.