Modern Vespa

I'm working on a P200e and could use a little help. I rebuilt the engine. All stock, except I did match/enlarge the carb box to match the carb and the engine case. The carb is a 24/24 with stock jetting 55/160 idle 160, BE3, 116 main. Has autolube. Timing is at 23 degrees BTDC. It idles well, plug is dark brown, but it's a little rough around 1/3 throttle.

Any suggestions on how I might smooth it out?

Have you turned your Air/Fuel mixture in/out to 1 1/2 turns or thereabouts?

If that doesn't do it, maybe a richer Idle jet, now the that the carb and box and inlet are flowed....

You got me on the right track (I heard richer jet). I upped the main to a 120 and that took care of most of the roughness. I'm thinking it needs a 122, but I don't have one and Scooter Mercato is sold out. I'll have to go as is for now... Thanks for getting me on the right path!

With the issue at 1/3 throttle I think I'd focus on the mixture screw for that transition mix rather than enriching the whole upper circuit

Fuel was the issue! Not the jetting or or the idle screw, it just wasn't getting enough fuel. Barely flowed out of the tap, just enough to idle. The photo of the fuel tap tells the story. The tank was clean and looked like new, so I never thought to check the fuel tap. I switched out the plug, cap, wire, coil and double checked the timing before I looked at the fuel tap. Always the last thing you check...

Good find!

Glad you got it sorted!