spark plug burnout

i know this is the wrong forum and all. but thought i would ask the yamahamer gurus.

i've got a 70's yamaha enduro 500cc. the ignition has points but works off the old magneto system. it doesn't need a battery to run. but one is in there anyways. they only cost $5 for batteries.

here's the dillema.

spark plugs don't last at all.

i can ride the bike for half hour. then have to change plugs.

if i fire the bike up and shut her off. have to change plugs to fire up again.

i replaced the igntion coil winding inside the magneto to get it running. along with brand new points and condensor. the bike is wired properly according to the book. the magneto has two coil windings inside. one for lights and charging to which the lights aren't there anymore. the other coil is the actual ignition coil. so the only thing electronic on teh bike is the igntion system which runs of the one magneto coil winding ONLY.

the spark plugs are the proper number according to teh book. the bike has the proper spark coil according the parts fischer.

any thoughts as to why the plugs won't last???

it be nice to have a decent weekend of riding in the dirt on one plug instead of having to buy 20 plugs just to get me by.

 

Post up a picture of the "bad" plugs.

Id say you had a rich mixture without looking but if they are black and "sooty" you should lessen the gas mixture on the mix screw.

Like I said put up a picture.

 

If you install new Spark Plugs into an Engine; and 20-minutes later, ... all your Plugs are Fouled, ...
Man, you got something Fowling Plugs that might be other than Mixture Related.

See what you got with a Compression Test?

What does it look like behind you, when you run it?

Blue skies, ... or Blue clouds???

 

the bike is a 4stroke.

the plugs are losing spark. they aren't sooty. there is no cloud of smoke.

they just flat out lose spark.

install plug. fire bike up. immediately shut off bike. no spark. change plug again. fires right up.

OR

install plug. fire bike up and run for about 30 minutes before dieing on it's own.

basically the plug can burn out in 2 seconds if the bike is shut off immediately. or it will last 30 minutes if the bike is kept running.

something is burning up the conductor material inside the plug shell would be my guess. what i don't know.

the bike was used 4 years ago. been sitting since. i'd like to put it to use some day but not at the expense of plugs everytime i want to ride it.

i'm thinking the spark coil is somehow producing higher then needed voltage. but i don't know how it would happen. and so far there hasn't been any used coils to be found.

 

Two things:

Rick, please move this to "other motorcycles" it may get interesting.

My vote goes to a possibly incorrect condenser. OR, the magneto needs to use its "charging" circuit as a voltage regulator, and without it is producing an unregulated voltage.

 

Maybe try 5k Plug Caps? If they aren't already

 

Ohm a new plug then ohm out a non working plug. Take one of the non working plugs and bust the ceramic off of it. Take pictures

 

I'll bet they're fuel fouling or the insulators are cracking. Result is the same either way - shorted out, not burned out.

I bet if you hold one of your "bad" plugs 1/4 inch from the engine and kick it over you get spark from the plug to the engine.

 

Did you get to the bottom of this problem? Inquiring minds want to know !