not sure about the guzzler don't even know wha tthey are, but if its pulsing, i would maybe think that there a point where its losing its vacuum suction, and the vac level fluctuates. as far as you were describing the vacuum starting at 20, down to 15, then down to nothing.........i bought a 78 years ago and learned this same way. 25 overheats them, i ran mine 25 first year with same thing happening, they overheated and would not slide freely in and out of slots so many days i had to open housing and free them up in am, i kept trying this and eventually same thing happened ended up at nothing. i believe they overheated and became damaged so i bought new ones for 75 bux online and ran no more than 20, ran fine for past 3 years. mine was rapping pretty good as they were sticking since when they stick they lose contact with housing and when enough centrifugal force is applied (about halfway thru housing) they slide out slamming the housing creating the "rapping" noise many speak of. get new veins, make sure housing is smooth burr and nick free. it only takes 10 minutes to change them, soak newones in oil overnight