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SteveP

Spark Plugs

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SteveP
Whats the deal with SPARK PLUGS. As Ducth noted in thread 3622 both the briggs and kolher ran better after he put in new plugs. I have a 16hp Vangaurd which "boggs down" and the governer pulls it down the RPM's at full throttle but idles fine. I'm going to change the plugs after work and see what happens. What I'd like is someone to explain the "Tech" end of why the plugs appear to have good spark but produce these "funny" side affects. Thanks Steve

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dlcentral
Steve, I don’t know if I can answer your question from a technical point. But it is very interesting to use a test machine that permits you to watch a spark plug firing under compression. Many times such a test machine will show a perfectly healthy spark until pressure (compression) is applied. As pressure is increased, the spark may stop jumping the gap and start traveling down the center ceramic insulator to the plug body. Build-up of fuel additives, carbon, or even condensation on the insulator will conduct electricity. Since electricity takes the path of least resistance, deposits on the insulator may have less resistance than the gap and the plug stops “firing”. It is important to remember that electricity will travel the path of least resistance. When a plug does not fire the electricity has to go somewhere. That may mean arching at the coil, wires, etc. Continued electrical arching will produce a trail of carbon so that even when a new spark plug is installed the electricity may continue to take the “wrong path”. As Bill (Sandy Lake) suggested in thread 3622, it is wise to replace plugs before they go bad. Plugs are relatively inexpensive insurance for proper performance. As for why my B&S needed the choke pulled out, and doesn’t now that the spark plug has been replaced…….. you’ve got me..! It may be coincidence, or it may take someone like Al Eden to offer a possible explanation.

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dlcentral
Steve, One other point. Always examine old plugs as they are removed. They are "windows" to the engine and can "tell" a lot about overall engine performance, and specific cylinder condition. From an old spark plug you can tell if an engine fuel mixture is too rich or lean. If the engine is running too hot or cold. If the engine (or cylinder) is burning oil. Or, if one cylinder is running differently than the other(s). Pick up a free spark plug brochure with pictures from your local parts store.

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RickA
In my line of work, I deal with spark plugs on a daily basis. Our engines run thousands of PSI in our combustions chambers. If you notice on new spark plugs the edges of the center electrode and the ground electrode on J type plugs have square edges. When a spark plug gets old, the edges on the electrodes become rounded. As stated in other replies, the spark will take the path of least resistance. On new plugs that path is from one sharp edge to the other. When the edges become rounded the spark has a more difficult time jumping the gap and will try to find an alternate route like through plug wires or across build up on the spark plug insulator. Also as you increase the load on your engine the cylinder pressures increase which increases the air resistance between the spark plug gap. Running an engine with a lean air-fuel ratio will require more voltage than an engine running a rich air-fuel ratio to jump the gap. You want to talk spark plug problems, try running an engine at 32:1 AFR and 5000 HP like we do here at Waukesha Engine.

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dlcentral
All I know is my Briggs and Kohlers only fire under 150 or so psi those hi comp tests don't apply here.These ain't top fuel dragsters!lol! I personally like AC and Autolite over Champs.There will ALWAYS be problems with Champ plugs but very rarely the other 2 brands IMHO of course.

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