industral air 3 cylinder 60 gal. 8 hp - slows down then speeds back up

When it starts up it runs fine after a few minutes sound like slows down then speeds back up no belts are slipping Does this every time i use it. Amp does not drop

___________________
Bill says...

From the sounds of it the load seems to changing.

Have you checked the intake filter to make sure it isn't clogged up?

Take the line off from the last cylinder to the tank. Any change in operation?

Cheers,

Bill