Vintage Synth Repair

Hi have just joined this group and hope someone can help.
I have recently aquired a werlitzer organ in not bad condition for its age.I have cleaned it all up inside and out all is working ok except for the bass pedal 16ft symptoms are as follows:
rocker switch on press  pedal no sound after short while it sounds
but is muffled and bubbling then it may play ok then go off then do same again.
The 8ft will play ok for a short while them it starts to bubble like the 16ft.but will stay normal for a short time. The contacts at the rocker switches are all ok as is the bass pedal contacts.any idea`s how to cure it.What may be the problem.
The model is 555 with orbit synth and dancing cords.