Modern Vespa

I'm a winter driver with Piaggio Fly 50 2011 model. Starting from around 50F downwards, the machine fails to start when relative humidity goes above like 80%. Temperatures even way below freezing give no troubles if the air is dry. I've solved the starting problem by using a cheap 12V warm air blower towards the machine from the foot rest by opening the small plastic panel there.

But another humidity related problem is that when temperatures are at or slightly above freezing and humidity close to 100%, the machine tends to stop whenever slowing down from full throttle and then giving any throttle back. I bet the problem is that the carburetor develops icing at high air humidity and so the machine fails to get enough air if not at full throttle. At cold start, the choke limits the air flow even more so no wonder it fails to start. Wikipedia also gives 80% humidity as a threshold for high chance of developing carburetor icing so it matches: https://en.m.wikipedia.org/wiki/Carburetor_icing

So the only way to solve the problem would be to heat the intake air enough so that it's humidity always drops below that 80% threshold. Any simple ideas? I bet heating the carburetor itself would be a bad idea since internet says the carburetor inner temperature can drop like even 100F below intake air, so close to impossible to keep the insides above freezing temperature?

Silkolene Pro-FST is what you need! https://www.silkolene.com/motorcycle/fuel-additives/pro-fst/

USA stockist:

Tucker Rocky
4900 Alliance Gateway Freeway,, Fort Worth, Texas 76177,
817-258-9255
newdealer@tuckerrocky.com
www.tuckerrocky.com

Note, I've only had to use it in the UK on a few bikes, I've not sourced it from the stockist above.

That's not how the choke on your bike works. You don't actually have a choke, you have an enrichment valve, that richens the mixture.

Question kinda related to this- Do the Fly 50s have the same rubber diaphragm/slide combo as the LX carbs? Could the older rubber diaphragms be losing elasticity in cold weather cause poor running?

Always seems like there's a few hard starting/stalling posts in the winter months.

If every other vehicle you own is fuel injected, yes, it seems like it's hard to start. If your cars and trucks still had carburetors, it would seem about normal.

I'm surprised none of the aviators have explained why icing is not the problem.

I'm thinking the low speed jet in the carburettor is blocked.