I have been working on reviving an old tub I aquired with the purchase of a house. Anyway, one of the four jets seemed to lack the flow rate of the others. I tried adjusting it by twisting the knurled nozzle, but this neither increased or decreased flow. Now the jet has not only completely stopped but I can actually feel it drawing water. As far as I can tell there are not any obstructions. Any ideas as to what is going on here?

Any chance of getting a picture of this jet. Sounds like there is either something blocking the orifice or a gasket issue. What is happening is the water through the jet is not setting up a venturi effect, check all the jets for blockage of the small nozzle inside the jet, bad gaskets and loose jets.

I was able to remove to jet housing and found a large gasket plugging up the plumbing. One problem solved and another is found right. Thanks for the reply.