(1) For the purposes of this section "vehicle" means any motor driven contrivance used as a means of transportation or recreation off of public highways.

(2) Initial inspection. An initial inspection of the vehicle exhaust system shall be conducted to determine if the following defects or modifications exist:

(a) The absence of a muffler;

(b) The presence of a muffler cut-out, bypass, or similar device which is not standard or normal equipment for the exhaust system being inspected;

(c) Defects in the exhaust system including, but not limited to, pinched outlets, and holes or rusted through areas of the muffler or pipes;

(d) The presence of equipment which will produce excessive or unusual noise from the exhaust system.

(4) Vehicle operation. The vehicle shall be operated as follows:

(a) Controlled ignition vehicles. The engine shall be operated at a normal operating temperature with transmission in park or neutral. Sound level measurements shall be made at three-fourths (75 percent) of the RPM for rated horsepower ± 100 RPM of meter reading.

(b) Vehicles with motorcycle engines. The engine shall be operated at normal operating temperatures with the transmission in neutral. If no neutral is provided, the vehicle shall be operated either with the rear wheel or wheels 2-4 inches (5-10 centimeters) clear of the ground, or with the drive chain or belt removed. The sound level measurement shall be made with the engine speed stabilized at one of the following values:

(i) If the engine data is available, test the vehicle at one-half (50 percent) of the RPM for maximum rated horsepower ± 100 RPM.

(ii) If the engine data is not available, and if the vehicle has a tachometer showing the manufacturer's recommended maximum engine speed ("red line"), test the vehicle at 60 percent of the "red line" RPM ± 100 RPM.

(iii) If the engine data and red line RPM are not available, test the vehicle at:

(A) 3500 ± 100 RPM for engines with total cylinder displacement between 0-950 cc (0-58 in.3).

(B) 2800 RPM ± 100 RPM for engines with total cylinder displacement greater than 950 cc (58 in.3).

(c) Diesel engine vehicles. The engine shall be operated at normal operating temperatures with transmission in park or neutral. Sound level measurements shall be made at the vehicle's maximum governed no-load speed. If the engine is not provided with a governor, the vehicle shall be operated in the same manner as a vehicle with a controlled ignition.