prechermike wrote on 08/26/09 at 04:34:35:kennycreed wrote on 08/25/09 at 23:16:48:Try new spark plug, sometimes SOME PLUGS??? sparks fine when you earth it to the cyl head to test it, but for some unknown reason, won't spark when tightened down in cyl head and gets all wet with petrol.
P.S. Always use a new plug,,they work hard and are cheap enough considering the work they do
Kenny,
That is a true but weird thing that happens to my Honda Fourtrax (ATV). For some reason the plug will simply quit sparking under compression. It does not matter if there is petrol (we say gas) on it or not. Outside, grounded to the frame, the spark is strong and bright, but the thing will not start at all. Put in a new plug and away you go. I never heard anyone else say that, though.
There are two remedies to this problem.
We don't necessarily ALWAYS have a new spare plug at hand.
1) Pull the plug out and "dry it" with a lighter or a match - that's to burn any possible fuel residue away;
2) clean the plug with a nail file (excellent handy item, especially the ones your missus will discard) to clean any carbon residue;
3) open up the gap from the recommended 0.4mm to about 0.8mm (you guys figure that out in 64ths inch)
What this does is to avoid that over-rich air/fuel mixture will soil (wet, foul) the spark plug before the engine's even started.
However, the plug will still spark.
The other remedy (which works wonders especially when occasionally touring high-altitude places) is to change the plug with a 3 or 4 pronged spark plug.
The 3, 4 prongs NEVER fire ALL together, there's only one firing at any one time,
BUT
you can foul one, maybe maybe two, never all three at the same time, and every single successful spark cleans the fouled prongs each and every time.
Take care, though, that the spark will fire downwards rather than sideways, so prolonged use of such a plug (meaning, many months)
may result in a holed piston.
But, as a "once in a while" solution, it's magic...