Modern Vespa

A couple of recent threads have me wondering about the advantages of the 24.24G carb. I get the bigger air filter with the built-in venturi, but is there anything else? In particular, is the compressed intake passage a good thing? Or maybe that is the reason they had to put a venturi in the air filter in the first place?

Put another way, which would be better and why: a 24.24G, or a 24.24E with no air filter (just bellows to frame) and one of those MRP or Polini bell mouths?

I think what you're looking for is, the G is better suited to higher rpm. An E will run ok at higher rpm but a G would be better. They all max out jetting at about 20bhp. Run what you have.

What I have is a 20.20 with a P200 air filter. It has exceeded all my expectations, but the one thing it still won't do is maintain 70 mph up a hill. That is a safety issue if you're trying to use the freeways around here.

Part of what has me thinking is Mr. Freakmoped recently posted a dyno test where someone got about 19.5 hp out a 177 Parmakit and a Polini box. Port durations were not particularly high. Carb was a 24.24 but couldn't tell if it was a G or an E. Only things that stood out were no carb box cover, no air filter and an MRP bell mouth.

Thinking I might try stuffing some air filter foam in the bellows, replacing the air filter with a Polini bell mouth and seeing what that gets me.

Sadly, all that will have to wait. It is very cold here, and the roads are covered with so much salt that my Indian steel bodywork would just evaporate if I took it out right now.

I think looking for a set up to pull up a hill at 70 mph plus is a pretty tall order without some substantial modifications that the 24.24G I don't think will help with. I wish you luck with your adventure.

The stock filter is restrictive a vortex is better. I like PinascoVRX, bellows, no filter.
The usual problem with a lack of torque is lean jetting. They'll run for years with lean jetting, just not go so well. One lean clue is, it will do 70mph downhill but only 45mph up.
Once sure the jetting is good and rich. If still not quick enough, there's a long list of stuff to check/modify/buy.

Yes, 70 mph uphill is my final frontier.

Polini makes a bell mouth for the 20.20. Thinking I will start with that as a proof of concept. Where I live is one giant sandpit, so also have to work something out on filtration. I see Pinasco makes a foam filter that covers the underseat frame opening. Maybe that is the answer.

I'd say try a 24 (Pinasco or BGM) carb, but that will take you on another jetting adventure. If you're exceeding all expectations with your current setup, that sounds like it ain't that broke, so

Could not get the Polini venturi to work with a stock airbox.
The venturi doesn't fuel-initiate well, and you need a too-big mj at high rpm. For a both stop and go & tourer it was impossible to jet (anecdotal experience of 1).

It lengthens the bore, delaying the fuel trigger point. It's affect on fuel mix also isn't linear through the rev range.

Downdraft carb with air flowing across it vs a sidedraft carb with more air space in front.
There are big airbox covers like the Vespec to help with this.
https://www.scooter-center.com/en/carburettor-bowl-cover-vesptec-airbox-for-vespa-largeframe-with-separate-lubrication-px-lusso-1984-plastic-asa-black-vt1056?number=VT1056

Yes, I have seen that a new carb box cover might be needed.

Does anyone have a sense of how many horsepower it takes to push a Vespa PX/LML Star/Genuine Stella uphill at 70 mph? If the answer is more than 20, then I should just throw in the towel because I agree that is not possible with an SI carb and I'm not giving up my autolube.

for the 20/20 carb don't forget this one (the original? with idea stolen from hot rod scooters...)

https://www.shapeways.com/product/ZFBJ7HCAE/20mm-largeframe-vespa?optionId=451888&li=shops

In line with this discussion, VMC has come out with a venturi carb box. It is a little spendy. Although designed to match up with a 26.26 carb, a 24.24 can be reamed out to work. A 20.20, probably not. Obvious concern would be clearance to frame. It will be interesting to see how that works out.

What I find most interesting is it tends to validate my idea of replacing the stock airfilter with some filter foam stuffed in the bellows. Based on what VMC is doing here, I think a 1 cm thick disc of 30 ppi foam treated with filter oil would flow nicely and exceed the stock filter in terms of protection. If 30 ppi foam proves too restrictive, the foam is also available in 10 ppi. Looks like the VMC kit has one of each.

Got a little more winter to get through before I can put these ideas into action.

https://avotecnica.com/nuovi-prodotti/3551-air-box-vmc-venturi-per-vespa-large-frame-125150200-.html

A 20 carb will work. You'd just have to open it more vs a 24.
Might even run better, since you can venturi-fy it deeper.