Hello, it sounds like a leaky knife valve in the regulator.  Simple test:

Disconnect the roll drive chain so the motor can run freely.  Insert
a roll to cover the tracker bar.  Play at, say, Tempo 70 and push the
regulator all the way closed.  The roll motor must immediately stop
completely and stay that way until you let go of the regulator.

You will find that it does not do this, and it either means that it
is not regulating because of a leaky knife valve, or that it is being
bypassed by the rewind slide valve not being adjusted properly or
warped.  See if you can adjust this first.

I assume that the regulator cloth is airtight.  Either way, you will
have to open the regulator.

Regards,

Bernt Damm
Cape Town