P125x Dies, no hot start

I just purchased my first Vespa (1980 P125x) Starts on third kick cold. Seller says he just rebuilt the engine and it seems to run pretty strong.

Problem is after I run about 5 blocks it tries to die. There is a flat spot when first twisting the throttle then it picks up. In the event the scooter does die it most likely will not start when it is hot.

I have drained fuel and put in new, installed a new properly gapped plug, and cleaned out the carb. It acts like maybe it is running rich and loading up. I hate to mess with the mixture tho.

Any help is appreciated. I have no known Vespa mechanics in the area so it’s just me, this forum and my Haynes manual.

Regards,

Nightporter

A flat spot on the throttle sounds like jetting/mixture probs in the carb, check thr haynes for the mixture screw settings then manually adjust the idle to a decent tickover that will still react to the throttle. You could also have an air leak in think but that could be on either side of the engine, what colour was the plug when last checked.
:shoot1:[:dance3:]

Do you leave the choke on?
have you blocked the air inlet under the seat?
is the plug wet?
start off with the simple ones! ;D