nklr spark plug puzzles shade tree mechanic

[Chris Norloff]

Thanks for the explanation Mike. I knew there was something about getting more voltage to the plug when you just held the wire close, but I couldn't put it together. Your explanation is going in my permanent file. I also like the history of the Champion spark plugs. best, Chris Michael Martin wrote:

> Hi Robert, > > When the ignition system supplies voltage to the plug, if you could look at the voltage versus time on an oscilloscope, you'd see that the voltage rises at a fairly steep rate, but not quite a vertical line. The defective plug, when the wire was attached, had deposits which would bleed the voltage down as it tried to rise. Thus the voltage would not get to the value it would take to jump the spark gap inside the cylinder. Although this gap was much less than the 3/4 inch you saw, the fact that the cylinder pressure is much higher than atmospheric pressure meant that it took a lot of voltage to jump the gap inside the cylinder. If you had re-gapped the plug to the recommended value, the voltage requirement to jump the gap would have been reduced and perhaps the engine would have run. > > When you pulled the spark plug wire loose and held it away from the plug, the voltage would not bleed off. It could keep rising to a value that would jump the 3/4" gap you saw. At that voltage value, it would also jump the gap at the spark plug electrode, causing the engine to run. > > Years ago, Champion made spark plugs with a gap up inside the ceramic insulator. They called this a "booster gap". These spark plugs were more resistant to fouling. I used them in my two-stroke Yamaha back then. > > I hope this makes sense. > > Mike Martin, > Louisville, KY > > > > > ________________________________ > From: Robert Waters > To: DSN_KLR650@yahoogroups.com > Sent: Monday, August 3, 2009 3:50:30 PM > Subject: [DSN_KLR650] NKLR spark plug puzzles shade tree mechanic > > > > Yesterday, a neighbor was having trouble getting his small push mower > started. I went to help and the first thing I did was hold the spark > plug wire out away fromt the plug while he cranked it. It started > immediately. Strangely, when I put the wire back on the plug the engine > would quit firing and begin to die. But I could hold the wire as far as > 3/4 inch from the plug and the engine would run just fine. I could see > no spark at all but the sun was shinning, which probably explains that. > > I pulled the plug out and the electrod in the middle was pretty much > burned up. I replaced it and it ran fine. But I have no clue why the > engine, with the old plug, would only run when the wire was held out > away from the plug. > > Any ideas? > > Robert Waters > > [Non-text portions of this message have been removed] > > > > > > > > [Non-text portions of this message have been removed] > > > > ------------------------------------ > > List sponsored by Dual Sport News at: www.dualsportnews.com > List FAQ courtesy of Chris Krok at: www.bigcee.com/klr650faq.html > Member Map at: http://www.frappr.com/dsnklr650Yahoo! Groups Links > > > > >