Modern Vespa

Dumb question but how long does a spark plug last? Do they come under the theory "if it ain't broke don't fix it". TIA

2-stroke engine: plugs work fine until they suddenly get irretrievably fouled just when you're farthest from home. Carry a spare.

4-stroke engine: plugs may last forever, but I'm always pleasantly surprised at how much better my scooter works after I put in a new plug at about 4000-6000 miles or so.

YMMV 8)

JK mines only 3 1/2 years old. Had to have the coil changed back then because the SP kept unseating itself when i'd hit a bump. We have a lot of them here. I guess over time it caused the plug to not fit in tightly. When i take him in at 50,000 miles i'll add this to the things that need to be done with my fluid changes.

Judy, my reply was a bit tongue-in-cheek, especially in regards to 2-strokes.

Four-stroke plugs seem to degrade gradually; it's not really noticeable until you put in a new plug and right away your scooter starts easier and gets better gas mileage. A spark plug costs about $6, so why not?

Spark plugs are wear parts. The "sparking" actually wears the plug, albeit slowly. So even in ideal conditions it's good to change the plug once and a while.

I do the belt, rollers, valve check and spark plug at the same time

Iridium plugs will go a long time.
Changing it out every major maintenance is pretty much how I go about it.
Less likely to be forgotten.
But I also use iridium in case I do happen to forget.

One thing I try very hard to avoid is the plugs that have the threaded end on them.
Had one give me all sorts or problems on my GTS; better off to get the sort with solid ends.

Thanks so much. I'll treat him to a new one at 50,000 miles. He's earned it. Have 48,600 miles on him now. 8)

Iridium is worth the small extra cost.

Bumps will NOT cause a properly installed spark plug to come loose. Also, changing the coil has nothing to do with spark plug retention. Did I miss something or is someone thinking they can pull one off on you???

No one can pull the wool over Judy's eyes. She did have a problem with the threads on the spark plug causing it to come loose and eject itself. Can't quite remember why the coil/cdi unit was changed but I think it was causing some misfiring even with the plug sorted out. No doubt she will be along soon to update you.

No the guys over here (not m mechanic) must of not seated it properly. Overtime it might of caused the coil wear down a bit. I probably didn't need to replace it but i didn't want to chance it.