This paper describes the combustion properties of the amino-substituted guanidinium 4,4,5,5-tetranitro-2,2-biimidazolate (N4BIM) series, including the bis-mono, di and triaminoguanidinium salts. These salts are of interest as propellant ingredient additives, and in particular, the bis-triaminoguanidinium salt of N4BIM displays excellent burn rate and combustion behavior. Our combustion studies have shown that TAGN4-BIM displays a fast burning rate and has the lowest pressure dependence exponent yet measured for a triaminoguanidinium salt.