Cal. Code Regs. tit. 14 § 1242
Mse. manufactured prior to July 1, 1978, which do not meet the minimum performance standards in 14 CAC 1241-1241.2 shall be equipped with a spark arresting device, installed in, attached to, or constructed as an integral part of the exhaust system, equipped with a woven screen with a maximum opening size of 0.0232 inches (0.584 mm) and is constructed of 0.013 inches (0.330 mm) or larger diameter, heat and corrosion resistant wire or has a usable life of 50 hours or more. The spark arrester will be considered in compliance with the requirement provided the total effective exhaust area (total area of openings) of the screen is not less than the 125% of the engine exhaust port area. The exhaust system shall be constructed to permit easy removal and replacement of the spark arrester screen for field inspection, replacement and cleaning.
Cal. Code Regs. Tit. 14, § 1242