Hawaii Revised Statutes Division 1. Government § 291-24

(a) Every motorcycle and moped moving under its own power on a public highway shall at all times be equipped with a muffler in constant operation to prevent any excessive or unusual noise and no such muffler or exhaust system shall be equipped with a cutout, bypass, or similar device. No person shall modify the exhaust system of a motorcycle or a moped in a manner which will amplify or increase the noise emitted by the motor of such motorcycle or moped above that emitted by the muffler originally installed on the motorcycle or moped except a motorcycle or moped that:

shall not be required to be equipped with a muffler.

(b) As used in this section, “muffler” means a device consisting of a series of chambers or baffle plates, or other mechanical design, for the purpose of receiving exhaust gas from the engine of the motorcycle or moped, and being effective in reducing noise.

(c) Whoever violates this section shall be fined not more than $100.