Rough running at low speed could be the prop, but since you just rebuilt it???
Hook up a hose and see if there's any wobble.
Then remove the prop and see if the shaft has any wobble.
The low speed jet in the carb is more than likely the problem.
To set the low speed jet.
Warm motor and running and in gear.
Can be done not running, results will be close.
Top of the carb, a slotted screw.
Initial setting is 1 and 1/2 turn out from lightly seated.
As it runs, turn the screw in 1/8th turn and see if it makes any difference in the way it idles.
Repeat this every 10 seconds until the motor stumbles, kicks, stalls.
Then out 1/2 turn.
Important to wait the 10 seconds between turns.
It allows the motor to burn the fuel in the system at the new rate.
These motors can run on 1 cyl and run fairly well.
Do a compression and spark test.
Oh yea, WELCOME!!