What was found
SUPPLEMENTAL INFORMATION, ATTEMPTED TO START APU BELOW 10000 FT FIRST ATTEMPT FAILED. UPON SECOND TRY STARTED NORMAL , HOWEVER VERY STRONG FUEL SMELL IN A/C AIRCRAFT. REMOVED FROM SERVICE, INVESTAGTED APU BAY FOIR FUEL. NONE FOUND. STARTED APU SEVERAL TIMES OPS CHECK GOOD IAW AMM 49-10-01. OPERATED BOTH PACKS NO ODOR EVIDENT. SUSPECT RESIDUAL FUEL FROM 1ST START ATTEMPT CAUSED MOMENTARY ODOR. OK FOR SERVICE. R/R APU FUEL CONTROL UNIT IAW AMM 49-31-00-06, OPS CHECK & LEAK CHECK GOOD FOUND APU HANGING 25% DURING START UP NO SMELL NOTED IN CABIN.