MIA83FA064

The plt & a prospective buyer/passenger were on a local demonstration flt. Prior to this flt, the acft had been parked for nearly 1 yr. Since the last annual inspection on 1/12/82, it had been flown only 66 hrs. During the preflt, the plt found the fuel tanks between 1/4 full & empty. The sumps were drained, the main tanks were filled, then the sumps were drained again. After takeoff, the plt leveled the acft at 1500 ft in a cruise configuration. Shortly thereafter, the left eng began running rough, backfiring & losing power. The plt turned back toward the arpt, but the eng lost all power & the prop was feathered. While returning, the right eng's cylinder head & oil temp began rising above the red line. Subsequently, it began losing power & a wheels-up, forced landing was made in an open field. An exam revealed that both engs were out of time, firing was intermittent 1 distributor block on the left eng was burneddue to incorrect timing. Also, the left turbocharger gate was stuck open & the left fuel filter was partially clogged.