Modern Vespa

ive got a 28mm dellorto with 2 fuel tanks the stock one and a legshield vbb glovebox welded into a tank. i dont have a battery but it says they will run off ac? should i go mechanical or electric?

I can't answer your question, but this: is cool!

they are 301 bucks from sip
http://www.sip-scootershop.com/EN/Products/90824000/Legshield+fuel+tank+VBB+tool.aspx

I've run both the electric and vacuum fuel pumps and it really comes down to what's easier to tap for power.

If you have 12VDC then the electric pump is easy to wire in. It's also easy to switch on an off so you can use it to refill your main tank from the aux tank with no other change in plumbing.

If you don't then you are left with the vacuum operated pump. This uses the pumping of the crankcase to power a diaphragm pump. That requires adding a fitting that on the crank case side of the reed or rotary valve. This kind of pump will always be running and produces more pressure than the carb can handle so you need a return line. A return line with two tanks can be tricky to pull off without over filling one.

The other factor to consider is the level of your cab relative to both tanks. If you need the pump to assure good flow to the carb then you will want it running all the time with a T from the pump outlet to allow the needed fuel to the carb with the rest going to the return line.

yeah i was thinking the exact thing while i was out driving. i think just the aux tank with an electric pump with a on/off switch wired to it is probably easier and better becuase id need like 6 tees and 2 returns plumbed in and tapping my manifold blows. i dont have my tap and die set here anyways. i think the SIP 12v pump doesnt put out enough pressure to overflow my carb. i only have 12 ac though but it will run a light i don't see why it won't run a pump

I'd definately go for the vacuum pump. It is a lot simpler setup, and I have seen them mounted on top of the intake manifolds together with PHBH or similar carbs. This means if they fail you can just reconnect the original line without any more fuss. Just make sure the pump is able to move the gas all the way from the glovebox to the carb.

You need a return line with the electric pump as well, but it only needs to loop around the pump. It doesn't have to go back to the tank. You just put a thinner return line or some sort of restriction in there and you will have all the flow you need.