Modern Vespa

Been reading up on evaporative canister removal and general poor running problems, as my GTS threw a code (flashing engine) a couple of weeks ago (was running rough). So, after having local Cespa dealer evaluate rather than remove the evap system I simply plugged the nipple at the engine and towards the tank I added 2.4 feet of line to allow overflow down towards the ground. Note that the line that was originally connected to the tank (between the tank and the first valve in the evap system) had fuel running out of it (only about 1/4 of the tank was full)!

Anyway, after taking the rear tire off (getting new tire after big flat) I started thinking about heat and the location of the fuel tank. So, it's directly above the muffler, right anbove the water pump, and right next to the engine. I wonder if those that have been having problems with stalling and rough running in the heat have considered this?

I wrapped the front of the muffler with heat wrap and then I put a high heat reflective, sticker backed material between the tank and muffler and between the engine and fuel tank.

My understanding is that hot gas is not conducive to good running. Anyone else had experience with this? I'll be out riding in 90 degree (F) heat over the next couple of days and let you know what I discover.

If you have filled up to the brim (not even overflowing) with a hot engine, then go a short distance home, the fresh cold fuel in the tank will expand and start to go down the overflow pipe when you park up and leave the bike for a while. This will upset the Evap Crap the next time you use the bike.

Yes, it's a piss-poor design, and yes, expanding fuel is as much a problem as overfilling, possibly more so in some cases.

Hot fuel isn't a problem in itself - it will reduce efficiency by a miniscule amount, but you'll never notice.

Cespa dealer ?

Oops! Nothing derogatory meant. 😊 just that the c and v are pretty close on my tiny phone keyboard.

I actually have never had fuel spill out of my Vespa 300. Maybe it is to darn cold here in Minnesota to have the problem. Further, when I fill up I am usually off on a long ride that sucks up the fuel.

Bob Copeland

If you haven't removed the Evap Crap, you won't have had fuel spill out of the overflow anyway. It just clogs up the canister, which starves the engine of some air.

If you've never had fuel spill out of the top of the tank filler because of mal-adjusted fuel nozzles then you have been very lucky indeed - or you've taken an age over refuelling by going tip-toe slow with the fill.

A US 2013 Vespa GTS, did it already have an EVAP-system?

Oh yes. Our 2009 and 2010 GTSs certainly did - for a short while! It was mandated here before it was in the EU.

This may explain why the Stella pees a little but only after a fill up. May even explain why it bogs sometimes at high speed under full throttle.

GREAT ... one more thing to check into.

Thanks, Jim.

As Jim observed, this has little to do with "hot" gasoline. How many 10s of thousands of GTS 250/300 with an evap system operate satisfactorily at 90 degrees F.

It seems related, as when fuel in the tank heats up doesn't it expand and overflow when full to top?

Regardless, my Vespa runs better after shielding the tank from excess heat. Just like after I wax it 😂

Waxing anything always makes it run faster, cooler and more efficiently. The 1st law of thermodynamics describes energy efficiency as the ratio of desired output to required input. You put the work into the waxing (input) and your overall efficiency improves (output).

Science.