Modern Vespa

Recently, I noticed that some of the major brands of both spark plugs and belts are being made available on a wholesale level at prices that remind me of a $50 Rolex Watch or $25 Louis Vitton Handbag. They are beautifully packaged, and look just like what they are supposed to be, but I've seen quite a few of them that even spark when you test them out of the bike, but won't ignite the mixture under compression.
So if you are going to stick with the brands you've known and trusted, I would advise you to buy them only from someone that you know gets them from the Manufacturer, and not someone who gets them from a distributor who may or may not get them from the manufacturer. Most Motorcycle and Scooter shops buy them from distributors. Many of the large auto parts chains deal directly with the manufacturer, and either stock, or can order the plug you need.
I have started using Nippon Denso plugs in my shop, They are the OEM brand for a number of Japanese Auto and Motorcycle manufacturers, I'm pretty sure they make some parts that are in Piaggio products and nobody has offered to sell them to me for 75 cents each. They have been very reliable, so I thought I'd share the part numbers with the

Standard Vespa 4 Stroke U24ESR-N , #4126
GTS that takes a two electrode sparkplug U27ETR #4155

An advantage of these plugs is that they have the screw end, so you can get a better spark plug cap and stop worrying that your spark plug wire fell off. Or you can get little aluminum replacements and continue to use the spark plug caps that were improved on several decades ago.

Thanks for sharing.

Iridium here

perefect

^^^Good stuff! $4.54 on Amazon. A good item for a free shipping add on.

This is good info, thanks

Same here IU24.

Denso Iridiums (and "normal" Denso plugs) can be had at Toyota dealerships (parts can cross-reference) for very little cost.
LOTS of them around.