Modern Vespa

hey all...I've got a 50cc 2 stroke.
I'm chasing something anomalous...and I'm looking for some thought input.
On the stand, without a "running load"..not riding it, it starts, idles nicely and revs to the moon.. very responsive at the throttle..rear wheel is spinning crazy fast!
When I go for a ride, it revs up and starts 'across the intersection' and then drops off...then picks up again and revs up.
I just removed carb and cleaned completely...wires through the jets and orifices ... soaked in cleaner..blew air, etc. I'm confident it's clean..I think.
New air filter, fresh plug, e-choke is getting current and pulling off.
I've got the air/fuel set out 1.75..(highest revving) (I'm going to turn it a little and check that again)

Caveat: I DID replace the front rollers with .5g lighter. 6.5 was stock...I tried 6's to alleviate the uphill drag that used to happen.
Could THAT be an issue?
I hear you.."put the originals back in a test it!"
I can't. I dropped 2 of them and they broke. (They're made of brittle Bakelite)
A guy local to me suggested a faulty stator?
Any other thoughts?

Well, im not sure why.. because if i recall, it used to run ok.
I removed the body work… again.. removed, disassembled the carb and cleaned everything.. again. Then I dialed in the air screw. Its now only 3/4 out… but it runs fine and the plug isn't too black or sooty.
I'm calling it done!
Thanks for listening

check the petcock and the vacuum hoses connected to it.....could be a carb starvation problem, but could also be a ignition problem, easy thing is to get a new sparkplug, and see that al connections sits snug and free from corrotion.

Thanks for the tips.
New plug,
vacuum line to/fro fuel tap 'sucks'
Fuel line from tap blows..hard.
Ducati coil sparks… HARD,
I had to put a new reg/rect and starter relay. It had been in 'un-prepped storage' for years, hence the carb, tank, battery, etc.
Someone had suggested the stator…and that feeds the ignition.
I'll see what it does tomorrow..after i R/R the tires.
Thanks.

Dialing the mixture screw into 3/4 turns suggests the pilot jet is too small or partially clogged. Normally, the adjustment falls between 1-to-3 turn out.

I think you're still running the 12mm Gurtner carb? I'd have to check which pilot it uses; mine went on the shelf when the decision to fit an Athena kit was made.

Your rollers are fine. If anything, they let the engine rev a touch more freely and allow the torque spring to hold you in low range a wee bit longer.

@az_lynch: Yes, its the gurtner 12.
Its a legit pita to pull the carb, but i will again, on your more experienced suggestion.
I've also read.. 1.5 and more turns out, as a baseline but since i got it smoothed out.. i let it go.. but i'll go in again.
Thanks!

Follow up..
Look.. i know "something anomalous" happened… but i dont know what.
Right now.. it runs great.. air screw back out to, maybe 1.25… plug looks clean enough.
The weather is still nice here in NoVirginia.. the Ducati's getting new fork seals and Kawasaki Concours is waiting on clutch parts… so, im going to just ride it!
Thanks az_slynch …Maybe i'll remove the bodywork later.