Thanks for asking. These things are subjective and somewhat based on opinion. The SI carb is what the engine was designed for and is most commonly used. Because of this parts are easy and tuning recommendations are easy to find. The main drawback is that you are limited to no larger than 26mm Venturi as it is the biggest size available. On a 225cc (or more) kit this may not suit your needs. It may also not suit some larger reed valve conversions. To sum up, I wouldn't use a non-SI carb a stock Vespa unless I had to.

Thanks Steve! I also use a 20-17 on my Super. It was standard on the Sprint 150 of the same era. You will likely find that you are a little rich with the new carb. I also swapped out the air filter for a larger P-series one. As always when changing carbs be sure to check the jetting when done.

Thanks, I’ll have to find another video on jet sizing and making the proper adjustments.

@@stevepaliobeis7216 Stock jetting for all bikes can be found at scooterlounge dot com. Just google scooter lounge stock vespa jetting. This is a good place to start if I recall correctly, I am using the stock Sprint jetting with a 100 main.

@@stevepaliobeis7216 I should add that I'm about 1K ft above sea level.

Hey, I’m back. Finally got my 150 back together and running, starts up easy, seems to idle fine, revved up nicely until it got warm then bogs down with throttle but still idled ok. Any thoughts? I don’t know much about the jets but there’s an E1 stamped on one and a 98 and 160 on the other. I’m at about 3000 ft elevation.

Thanks for the comment! Yes, of course. I am sorry that I forgot this at the time of filming. Have you seen the video I did on the Series 1/2 Lambretta (MA19BS7 I think) carb you guys are doing? Awesome -- love 'em.