Modern Vespa

I have a hopped up 66 Sears bluebadge that I'm trying to dial in:

Polini 130cc
Dell'orto PHBL 25 BS carb
Reed valve intake
Banana exhaust (some sort of Faco clone)
Electronic ignition

It starts and idles perfectly. 1/2 throttle to WOT it is a beast.

0 to 1/2 throttle is where it's uneven and sorta lurches. It feels like maybe it is starved for fuel.

Carb specs:
idle jet: 50
choke jet: 60
main jet: 92
slide: 30
atomizer: 266AQ
needle: D29 (clip at second notch from bottom)

Any suggestions?
From my research, I'm thinking I should focus on the needle and air/fuel mixture? Richen by moving the needle up by one notch?

Thanks in advance.

If you raise the clip, you are leaning it out by letting the needle sit lower! Not richening up 0-1/2.

I'd that makes things better, keep raising it. After that, you'll have to switch needles with a different taper/ wider.

Last edited by MJRally on Sun Jun 12, 2022 3:29 pm; edited 1 time in total

I've had really good luck using the slide to tune that exact area. Are you gurgling and four stroking, or is it a lean bog?

Do you mean raising the clip on the needle? It's my understanding that lowering the clip will make the needle sit higher. That's what I was going to try. Is that right?

Moving clip whichever direction pulls it further out of needle jet makes it richer.

Edited that for clarity. Was a typo.

Yes, lowering the clip will make the needle sit higher, which will richen 1/4-3/4 throttle. The needle physically blocks fuel from going up the main jet and into the motor. Once youre at WOT, the needle is so high up, only the main jet is metering things.

If you raise the clip, you lower the needle, which will leave more of it in/ physically blocking fuel at that 1/4-3/4 throttle range. That is leaning out that range. That works until its WOT.

Let me try to find a good youtube video explaining it.