Welcome to CoffeeSnobs [smiley=thumbsup.gif].
I dont own or have ever used an iRoast, and no doubt one of our many member/owners will offer up some first hand advice. Just from what you describe though, it sounds like the air-flow was being restricted by the faulty chaff-collector before, and now that you have repaired it the air-flow has increased to what it should have been all along. Heres some really good info on iRoast roasters here that might be of help to you...... http://coffeesnobs.com.au/YaBB.pl?num=1124115705
Maybe you just need to adjust the bean batch size up a bit to allow the roast chamber temperature to increase? Since Im unaware of the technical specs of an iRoast Ill leave this up to you and other owners to comment on. Hope the above thread helps you out though ;D,