LAX85FA238

After deptg & climbing to 4500', the plt & his plt rated pax noted a fuel odor & returned to the arpt to land. Bfr lndg,the plt called the tower (twr), but didn't advise twr psnl of the fuel odor or of a psbl prblm. As the acft was turning off the rwy, fire & smoke erupted in the eng compartment & spread beyond the firewall to the cockpit. The plt & both paxdeplaned. A twr controller saw the smoke & initiated fire/rescue response, but didn't use proper terminology. Fire dept psnl were dispatched aprx 1 min later. By the time they arrived, the acft was badly damaged. Most of the eng's fire damage was on its left side. When tested, svrl fuel lines/components leaked, but they had fire damage & the exact in-fltfuel leak was not verified. Fuel stain/discoloration was noted where the air throttle metering unit leaked at an o-ring. There was a fuel leak at the idle fuel adjustment screw, altho it was 'frozen' in a fixed psn. Also, Beech had rcmdd replacing the fuel lines every 5 yrs, but no record was fnd of their replacement during the last 5 yrs.