Modern Vespa

Obviously clogged jets is a thing, and I've blown pretty good sized chunks out of a jet before.

How the heck does crap, crud, dirt and shit get past that ultra fine mesh filter that sits above the float bowl where the fuel comes in?

Or is it somehow working it's way up backward through the system?

Lot of time is a build up of tiny tiny bits of dirt. Especially on a bike that's been sitting. You will get oil residues for the shit to stick to

If it's coming from the fuel system, there should be stuff in the sediment bowl underneath that mesh screen. Microns are often used in filter talk. The tank filter and that mesh filter seem to be more blocking small children/insects sized. Same for the air filter.

I think some of it is stuff the air filter doesn't trap that gets drawn in through the air corrector holes in the jet stacks, mixed with fuel and later settling to the bottom of the jet wells. My experience is that the idle jet gets clogged occasionally. Running a large Fram G1 fuel filter, against common wisdom, for nearly two years did not prevent a couple of idle jet cleanings. That idle jet hole is REALLY small. I keep a small brass brush bristle, with a small glob of tape on the end so I can find it, for roadside cleaning. Also a drinking straw to blow into the jet well. We do a good bit of dusty unpaved road riding. Mrs. Bart has learned the symptoms well and lets me know pronto.

I am not suggesting to run an inline fuel filter. It was an experiment.

Good stuff guys. That all makes perfect sense.

I was having chronic idle jet plugging until I cleaned my tank fairly thoroughly, even thought there are two filters between the tank and the jet. It helped quite a bit.

Like others, I keep a little bit of wire to poke in the jet, and on long, 100+ mile trips, I pack a small can of carb cleaner. If the jet plugs up, I can blast it out at road side and it generally works fine.

Hojo