What was found
APU PUTS OUT LOW DUCT PRESS ON STARTS, DOWN TO 18 PSI AT HIGHER ELEVATIONS & FLUCTUATES. RUBBER BURNING ODOR IS STRONG WHEN APU BLEED AIR IS ON IN FLIGHT & GROUND. INSPECTED APU INLET, COMBUSTOR, DIFFUSER & EXTERIOR. NO DEFECTS NOTED. INSPECTED BLEED AIR DUCTING IN AFT EQUIP BAY, NO DEFECTS NOTED. INSPECTED WATER SEPARATOR, NO DEFECTS NOTED. OPERATED APU & PACKS, NO RUBBER OR BURNING ODORS NOTED DURING 2 HOURS OF OPERATION. 34 PSI AVAILABLE START PRESS WITH PACKS OFF. MOTORED BOTH ENGS, START PRESS NEVER DROPPED BELOW 24 PSI. LEAK CHECK OF DUCTING GOOD. ALL WORK IAW MM 49-10-00, 36-10-00 & 71-00-00.