40 CFR § 86.425-78
Test procedures
June 9, 2020
(a) Motorcycle emission test procedures are found in subpart F.
(b) The Administrator may prescribe emission test procedures for any motorcycle which he determines is not susceptible to satisfactory testing by the procedures set forth in subpart F.
(c) Testing of any type with respect to any test vehicle other than that specified in this subpart and subpart F is not allowed except as specifically authorized by the Administrator.