Modern Vespa

Since I dont use my rear rack on my GTS I was wondering if anyone has ever mounted a small gas tank to it.Small plastic flat one and have it feeding the main tank as needed or a shutoff that could be used as a reserve. I know this is out side the box but could this be done?
Older Guy cant wait to see replys

Try searching the site for "auxiliary tank". Many folk who do longer rides just have a spare plastic tank on the foot board - you can actually buy stands for them to make it safer. The problem with having the tank right at the back is it's a bad place to place weight and, if it's connected to your fuel line, some joker might cut it for a laugh. The cannonball riders do some interesting things to let them ride further. Me, I'm quite happy to stop and stretch my legs when the fuel gets low.

Exactly. Anyone who burns through a tank of gas and doesn't appreciate a reason to dismount is made of some pretty tough stuff.

Good thought,very true
Older guy

Several riders in the Cannonball use auxiliary tanks.

Here you can see a few in these photos from Hyder, Alaska at the start of the 2014 Run.

Bill

A while ago gogogordy posted a pic of his BV350 with a Rotopax tank on the back rack.

^^^rotopax or 1qt msr fuel bottles...you can fit the msr fuel bottles inside a operator manual storage tube and mount the tube to your rear rack (link below)...people over on the tw200 forum did this all the time...i used the tubes for tools and mounted them on my rear rack

rotopax
https://rotopax.com/

msr fuel bottle
https://www.msrgear.com/stoves/backpacking-stove-accessories/msr-fuel-bottles

operator manual storage tube
https://www.agrisupply.com/manual-canister-large/p/80881/

tw200 forum mounting storage tubes
https://www.tw200forum.com/forum/performance-customization/212-famous-storage-tube-2.html#post9753

never seen any connected to the fuel tank though...how would you connect it?...if you had the external tank connected you would need a shutoff otherwise the external tank would overfill the internal tank since it's gravity fed and higher than the internal tank...also how would you know how long to open the external tank for so you don't overfill the internal tank?...you'd still have to open the gas cap to see the fuel level i imagine...would there be venting issues?

Two ways:

Connect fuel line from Aux tank to tank vent on the scooter.

Drill hole in fuel cap and install a barbed fitting run hose to Aux tank and block vent on scooter tank.

Both require EVAP System to be removed.

wouldn't you then need to vent the rotopax?...and how would you solve the overfilling problem?...could you just wye into the fuel line after the internal gas tank and install an fuel shut off valve...like a legit auxiliary fuel tank?...but that would try to fill the internal tank just due to gravity if you didn't install a backflow/check valve

https://www.amazon.com/Return-Check-Petrol-Diesel-Aluminium/dp/B06XK215S7/ref=sr_1_4?s=automotive&ie=UTF8&qid=1548692042&sr=1-4&keywords=fuel+check+valve

edit: just remembered we are talking about fuel injected bikes so getting the fuel to the fuel pump inside the internal tank is the issue so you would want to fill from the top

wonder if a dirt bike cap with a vent like this would work to wye into...actually i don't think these are water tight though...i think there is just a ball in there sitting on top of the tube to relieve any pressure that builds up

https://www.amazon.com/Breather-without-Valve-Motorcycle-10pcs/dp/B00ZUAI51Q/ref=sr_1_1?s=automotive&ie=UTF8&qid=1548692248&sr=1-1&keywords=dirt+bike+vent

Old Guy, I'm thinking old school:

Milk Crate, you can get some simple mounting brackets or Bungee Cords. Get a one or two gallon plastic tank (Depends on what fits in the crate.)

Or you can forgo the milk crate and just get the extra tank and bungee it to the rack.

^^^could probably pick up a gas tank from a dingy which would work well but probably won't fit in a milk crate

https://www.amazon.com/dp/B0053HOWUO/ref=sspa_dk_detail_7?psc=1&pd_rd_i=B0053HOWUO&pd_rd_w=o0BMi&pf_rd_p=f0dedbe2-13c8-4136-a746-4398ed93cf0f&pd_rd_wg=3berf&pf_rd_r=KE9T3V962KF8E9K527T9&pd_rd_r=33f2b6e9-2324-11e9-b177-15559c9dc0fd

if you just want a filler tank i recommend either 1 of these 2...both of which fit in a milk crate i'm pretty sure...i have both of these...

https://www.amazon.com/No-Spill-1405-2-1-2-Gallon-Poly/dp/B000W72GBC/ref=sr_1_1_sspa?ie=UTF8&qid=1548697578&sr=8-1-spons&keywords=gas+can&psc=1

https://www.amazon.com/Justrite-7225120-AccuFlow-Galvanized-Flexible/dp/B003PGRR48/ref=pd_bxgy_328_img_3?_encoding=UTF8&pd_rd_i=B003PGRR48&pd_rd_r=c2860aa9-2324-11e9-8b12-b5a7828cf626&pd_rd_w=ouy3M&pd_rd_wg=uU0jy&pf_rd_p=6725dbd6-9917-451d-beba-16af7874e407&pf_rd_r=J42Q064GVEJCFXXWZ96W&psc=1&refRID=J42Q064GVEJCFXXWZ96W

Acerbis makes an auxilliary fuel tank for motorcycles.
They come with a siphon kit that can connect to the fuel overflow.
As the fuel tank empties, the fuel runs through into the tank.
Just mount it in a suitable position close to the rear filler.

Personally, I would go the route of the tank secured to the floor panel over the battery (red arrow) as the large, high and far back position of the aluminum tanks (black oval) will change the handling characteristics a lot. Having the fuel can available means you could help your riding buddy who runs out. Notice also the extra MSN fuel bottle at the top case for that last pint of fuel...