slow down- you have to go through one step at a time

1. is the belt on right and somewhat tight ? or is it loose and
falling off ?

2. you have to rough up the capstan so it can grab the tape and move
it- I have an old RCA table top deck that needs capstan resurfacing at
least once a month, or it drags tapes

3. you may need a new motor

4. you may have an AC Motor, and have a capacitor in line with the
motor- if that cap goes bad, the motor will slow down after a few
minutes. I had a deck that both the cap AND the motor eventually
needed to be replace.

5. if you're over your head with this, or are not the hands-on
technical type- you have to send that to someone to get fixed- or sell
it/give it away/throw it away, and get a functioning deck. 8-track
decks have come way down in price on ebay, you can get a high end unit
in working condition, for under $75, and sometimes under $50