| If it's anything like the Boss BF-2 circuit, which is highly likely, one of those trim pots will control the maximum resonance. Tweaked too high it will cause self-oscillation.
Another will likely affect delay time. Too high a delay time will result in excessive degradation of the signal - which to some people is a positive.
The third one might be BBD bias, which you should have left alone as it is tuned in the factory for the best performance and nothing exciting happens when you tweak it.
Check out the wiki for my self-oscillating BF-2 samples.
__________________
niftydog
"My feet itch." Mike Patton | 
