I've found even when cleaning them with iso i lose a bit of power and they shriek like a banshee, however it may be that you haven't bedded the pads in properly some take a while but i've found that with new pads the best way to bed them is to ride about half a mile to a mile with the brakes on and getting them really hot, sometimes you can smell the pads burning but thats no problem let them cool on their own or chuck some water on them. If after all that they still dont work you've some how contaminated them which renders them useless.
