That can be due to combustion motor being faulty, the centrifugal switch inside the motor being faulty or the comb. motor air pipe being damaged/clogged.
Most often it is the motor or switch and since the switch cannot be bought separately from the motor, either way requires a new combustion motor.
Let me know if interested in ordering info. Would need an hvac tech to test everything to see which one is at fault for sure.
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?