Described herein are systems and methods for reducing cumulative deposition and unwanted secondary thermal reactions in pyrolysis and other thermal conversion processes. In an embodiment, a system comprises a device, referred to as a reamer, for removing product deposits between thermal conversion and condensation operations of a pyrolysis process. The reamer may comprise, but is not limited to, a mechanical reciprocating rod or ram, a mechanical auger, a drill bit, a high-temperature wiper, brush, or punch to remove deposits and prevent secondary reactions. Alternatively or in addition, the reamer may use a high-velocity curtain or jet (i.e., a hydraulic or pneumatic stream) of vapor, product gas, recycle gas, other gas jet or non-condensing liquid to remove deposits. Preferably, the reamer removes deposits during the pyrolysis process allowing for continuous operation of the pyrolysis process.