Decomposition of YBa₂Cu₄O₈ into YBa₂Cu₃O_{7- delta}+CuO in the silver-sheathed tape form has been studied. In these tapes, the excess CuO is expected to provide additional flux pinning centres and consequently to increase the critical current density beyond that of an equivalent conventional YBa₂Cu₃O_{7- delta}. Silver-sheathed YBa₂Cu₄O₈ tapes were produced by first using an oxalate solution method to coprecipitate (submicrometre to nanometre size) precursor powder that was then drawn into tapes by a powder in tube technique. From a series of investigations of the parameters for decomposition of YBa₂Cu₄O₈, the optimal time and temperature for processing these tapes were found to be 25 min and 915 degrees C, with oxygenation for 48 h at 450 degrees C. This procedure yielded the best J_c of 2.2*10⁴ A cm^-2 in self-field at 5 K. This critical current value is an enhancement of two orders of magnitude from the value obtained in as-drawn tape.