I've only ever had these chips where they've failed to produce any delay and give no output. The fact you're getting any effect suggests that your problem lies elsewhere. The first think I'd check is to make sure the DC voltages are all correct. I get plenty of older pedals where the electrolytics have high ESR. Sometimes they bulge, but this isn't always the case. A bad cap can give you serious signal loss, depending where it is.
Can you post a link to the schematic?