I have a bluebird aerator with a 3 horse briggs and stratton motor. It will idle fine, but when the RPM's are increased it starts to pulsate. It does this all the way up to full throttle. However, when the tines are engaged, it purrs like a kitten. Ive checked everything i can think of to no avail. Anyone have an ideas what could be causing the pulsating? Thanks in advance.