The only way to speed control those motors is by nature a kludge, and you have to be careful not to stall them, it involves variable frequency inverter drive and disconnecting the start circuit after it is up and running, Its not a job for a newbie, (no offence), and as I said carries a risk of the motor being damaged if it stalls.
No drive manufacturers will back such a system with a guarantee.
Hope you find a solution.
Regards Xena.