Modern Vespa

I'm wanting to install a 24/24G T5 carburetor on my P200 and i'm trying to figure out a baseline to start the jetting at. The P200 is all stock with the standard USA head, Sito+ muffler, and a 36 tooth short 4th gear. The scooter usually sees a fair amount of 55~65mph highway cruising for 20~40 miles at a stretch. The elevations that i ride in are mostly from sea level to 3000'. Ambient outside temperatures are anywhere from 50~100 Fahrenheit. As something to compare to, all my other stock P200s (with the stock 24/24E carb) are jetted to a 160/BE3/125, 55/160. Does anyone have some input on where to begin with jetting?

Start with all the T5 jetting and a big main jet and work down.

I'm not sure what all the original jets are in the T5, but i think the air corrector was a 185?..which i believe would be kinda lean. Some of the 24/24G specific air corrector jets that i do have on hand are 150, 120, and 185. I have the stock 50/100 idle jet as well.

One of my friends recommended a 120/BE1/125 jet stack and either 50/100 or 55/160 idle jet. I currently don't have any BE1 atomizer, just BE3 and BE4.

Stock T5 is 50/100, 120/BE4/110…

Also, from my personal experience, make sure you get a matching air filter. The normal ones for 20/20 and 24/24 won't mate properly to the top of the T5 carb, and modifying them to fit will result in a plethora of problems.

I'm glad you brought that up just so that information is out there. I do have a couple T5 filters on my shelf that i will be using, i just forgot to mention that in my original posting.

matching air filter AND airbox lid!!

the stock lid won't contain the mighty T5 airfilter!

(a Stella one is the same)

and the screws for the T5 filter are different as well

So what happens if you use standard P200 jetting in a T5 carb? Such as a 160/BE3/125 jet stack and 55/160 idle jet?

Temporarily i'm using the shorter T5 specifically length 120/BE4/125 and a 50/100 idle jet. How is this different from a 120/BE1/125?

The T5 carb is shorter and needs the T5 filter or Venturi. P200 jetting will be lean on either.

Post some sound recording of how it's running. No doubt it will need some adjustment.