Jointer doesn't run smoothly

My bet is that the motor is designed for 220/240 (single or three phase), but you're running in on 110 single phase. If the belt were slipping it would sound like the belt on a car (you know when someone starts their car and belt is loose and goes "Sccrreeeeeee" until the rev the engine and make the belt catch up to the pully).

The power in wood working motors is such that it should be very difficult to slow down the motor if you're feeding at a slow rate. But, if the motor needs 220 and you're powering with 110, then the motor will have no power (the magnets in the motor are matched with the voltage - and if you have the wrong voltage you won't get any power and the speed will be very slow).

Typically the "home" or "residential" tools only run on 110, but if you have a larger unit they can be wired for 220 or 110. If you bought the planer used, they may have been running with 220 and now you're powering with 110 (or vice versa). I'd do a quick google search for your unit to see what it's capable of. Or, just take the model number of the motor (not the planer) and search for that.

Typically, motors can be run at 110 or 220 for larger wood working tools. Inside the metal housing where the wire feeds into are a number of wires to connect to. These wires have numbers on them (either a tag or printed on the wire insulation) and you attach them a certain way for 110 and a different way for 220. Sometimes you can even change the direction of the motor - SO BE CAREFULL IF YOU REWIRE IT! don't power it up all the way on the first try. Just start it and then stop it while the motor is still coming up to speed. While the planer is still spinning (even though the motor is off) feed your board in slowly and you'll be able to tell which way the motor is spinning. If you get the wrong direction on your motor you can shoot boards across the shop (or out into the street if you're in the garage - like I did).