I've recently bought a second hand pfaff 335-h2 cylinder bed sewing machine & I'm having some issues with the presser foot. It isn't feeding the fabric through properly. The vibrating presser foot is working fine, but the fabric is just bunching up between the two feet & jamming. I've adjusted the tension on both feet and I did seem to get it all working for one very short test run, but now - nothing! What I'm noticing is that while the vibrating presser lifts between stitches, the presser foot doesn't. I've looked at the adjustment manual, the user manual, and the adjustment manual for the Pfaff 145 which is a similar, though flatbed, machine. Any suggestions greatly appreciated!