  We present measurements on a series of materials,
Li$_2$In$_{1-x}$Sc$_x$Mo$_3$O$_8$, that can be described as a 1/6th-filled
breathing kagome lattice. Substituting Sc for In generates chemical pressure
which alters the breathing parameter non-monotonically. $\mu$SR experiments
show that this chemical pressure tunes the system from antiferromagnetic long
range order to a quantum spin liquid phase. A strong correlation with the
breathing parameter implies that it is the dominant parameter controlling the
level of magnetic frustration, with increased kagome symmetry generating the
quantum spin liquid phase. Magnetic susceptibility measurements suggest that
this is related to distinct types of charge order induced by changes in lattice
symmetry, in line with the theory of Chen et al. [Phys. Rev. B 93, 245134
(2016)]. The specific heat for samples at intermediate Sc concentration and
with minimal breathing parameter, show consistency with the predicted $U(1)$
quantum spin liquid.
