Help Flat spot!

hi

i am running a px125 engine in a vespa super frame standard exhaust and 20/20 carb

and have a flat spot and tries to cut out  every time i pull away i have a 100 main jet and the engine tick's over nicely any ideas

jules

hi

yes the original was a 98 jet but its an autolube engine which is now pre-mixed in the tank so have gone up 2 jets from previous experiance,

the carb and filter are brand new!

i think the original main jet was the 98(why you have the 100?)

by the way try to clean up the carburetor and the air filter!