Modern Vespa

It looks like the tank is no longer vented. Stick that coupling you're talking about on, attach a piece of the same hose and run it to a spot that won't drip on the scooter or exhaust in case you fill the tank up to the filler neck. Air needs to get in as you use up gasoline.


cheers

Mike,
I've been tracking your project(s) and have got to say, I'm impressed. I've got a couple questions, but they'll wait until I've been reunited with my scooters. For now, who manufactured your windscreen? Also, I hope you've logged some miles, while the mods may be fun to do, they really can't compare to the ride!
Kudos,
Jim

It's weird different scooter cultures round the world.

Obviously theres a big scene over here in England, most wouldn't be seen dead with a screen like that, even with the weather we get over here.

You guys outside the US are missing the gist of this. The US evap system makes sure that fuel vapors from the gas tank never make it to the atmosphere. Unfortunately, the system on the GTS seems to be prone to failure, leading to high-RPM stumbles. It's not a kinked hose, there's a check valve that fails. You either have to replace the check valve or disable the evap system.

Follow the hose from the neck of the gas filler around the inside of the bucket area (with the bucket removed). The hose snakes along the left side. Find the point where that hose connects (to a thing under the left cowl) and cut the hose. You now have a conventional vent system, where excess fuel will drain to the ground.

cheers
Note that I am NOT advocating the removal of the evap system solely for the sake of removing the evap system. I am informing people how to get their scooter to run correctly when the system fails because of crappy design.

It's not so much that they run better without the evap system, just that the evap system is easily overwhelmed the first time you overfill your tank. On the GT, simply disconnecting the evap hose at the carb will remedy the problems caused, and allow you to reconnect it later if necessary. You could remove the cannister, but it'll only save you about a pound or two.

The GTS is a bit harder, because the clamps are harder to remove and because it appears to fail in a different manner, allowing vacuum to form in the gas tank. I think there's a valve that gets stuck, independent of the evap cannister, and requires removal of the gas tank vent hose from the valve.