I dont get it... the plug was getting a huge bright blue spark when i tested it. And it would fire up for 1-2 seconds then stall out. how is a new plug fixing this???
Not sure why, but for some reason I was under the impression you had already tried a new plug???
It wouldn’t surprise me one bit if a new plug makes a huge improvement… I’ll go back to something I posted earlier in this thread, “
A new plug can never hurt and often will fix problems seemingly not related.” And also, from
kmcinms, “
Firing under compression and firing in the atmosphere is two different events.”
Grounding the plug and watching for spark is not “testing” the plug, it’s testing the coil’s ability to make spark… you can do the same thing by holding the plug wire end while cranking the engine, but that can be a bit uncomfortable. Sure, if the plug has gone permanent “open” (like an internal break) there won’t be any spark, but just because there is spark doesn’t mean the plug is “good”. There’s a lot of different ways a plug can fail… compressed air/fuel and heat add a bunch of stress on the plug, which will cause problems not seen in open atmosphere. For example, firing the cylinder just a handful of times can raise the plug’s internal temperature enough to cause the center electrode to go high resistance/open, or cause an unseen hairline crack in the insulator to allow shorting. A classic example of a bad plug is when the engine will start just fine cold, and run just fine, but won’t restart when hot (although other things can cause this also); the plug’s resistance is increasing with heat and shutting the engine down causes it to sink even more heat from the cylinder head… end result is a plug that can’t make
enough spark to fire the engine until it cools off, which lowers resistance. An atmosphere of compressed air/fuel increases resistance between the plug’s air-gap… a plug that makes good spark in open atmosphere may make weak spark in the cylinder, or no spark at all. Adding more fuel increases resistance… have you ever had a car that would idle perfectly, but start missing under load?? Most often that will be traced down to a plug or plug wire with high resistance (higher than specified tolerances)… or a hairline crack in the insulator of either, causing a short as air-gap resistance increases in the cylinder.
I keep at least one new spare plug for every engine I own (quick count… 13); whenever I have
any sort of problem (even seemingly unrelated) the first thing I try is a new plug (heck, they’re cheap). I would have to say, best guess, at least 2/3’s of the time a new plug “fixes” it. Besides, ain’t nothin’ that will pizz-you-off more than screwing around with a small engine for hours, or even days, when five bucks and sixty seconds to replace the plug “fixes” it… yeah, been-there-done-that!
I use NGK spark plugs (shrug)....
