i have an 1980 DT125 that i have been restoring. took the carb out and cleaned it, new fuel cock, everything de-greased but keep coming up with the same problem. i use the choke out to start it and wait till it warms up and idles at about 2k and then when i put the choke in the bike dies. i can ride the bike with the choke out and it rides fine but once i put the choke in while riding and i slow down and downshift, the bike loses power and dies. anyone have any suggestions to try. thanks.

try cleaning/replacing the air filter.

new spark plug?

are the float height set properly?

did you give the carb a good clean out? the smallest piece of dirt may affect it.

i use an areosol carb cleaner then blast every hole with compressed air.

remove all the jets and do them separetly.

good luck

sounds like a classic case of pilot jet blocked, remove the jet can you see daylight through it. Further cleaning of carb would benefit you, ultrasonic if possible and blow through the circuits with compressed air. If you are going to use carb cleaner remove anything that has an O ring on it first.