In this paper, we strengthen two recent undecidability results of [9,10] about weighted timed automata, an extension of timed automata with cost variables. More precisely, we propose new encodings of a Minsky machine that only require three clocks and one stopwatch cost, while they required five clocks and one stopwatch cost in [9,10]. Key words: Weighted timed automata, weighted timed games, undecidability