Suzuki first used exhaust valves in 1985, using a drum valve that uncovered a cavity in the head or cylinder to add volume and length to the exhaust pipe, strictly at low rpm. In 1987 they employed a system that featured two large valves that had multiple functions. This system was used on the 1989-2000 RM80, 1987-2000 RM125, 1987-95 RM250. The wedge shaped valves was positioned at about a 45-degree angle over the exhaust port. The ATEV system is designed to regulate the effective stroke, exhaust-gas velocity through the exhaust port, and on 1995 and later models it controls the exhaust gas temperature. The ATEV system is self-cleaning in that the valves are scraped of carbon every time they move. Some of the early-model RMs suffered from broken exhaust valves when the stem would detach from the cylindrical wedge. That problem was cured in 1991 when the radius between the stem and valve was increased. The two common problems that occur with the ATEV are caused by the two following errors in assembling the system:

1. Too much preload on the spring. On the left side of the cylinder is a dial that controls the spring preload for the exhaust valve system. The preload doesn't have that great of an affect on the engine's powerband, but too much preload will prevent the valves from opening, which causes a lack of top-end power.

2. Crisscrossed spring. A centering spring on the right side of the cylinder, located on the rod, actuates the valves. This spring is commonly installed wrong. The spring tabs should be parallel when coupled to the lever and rod. If the spring tabs are crisscrossed, the valve travel will be limited and won't open fully.

In 1996 Suzuki redesigned the RM250 engine, going back to a design reminiscent of the 1987 model RM250. For this model Suzuki modified Honda's HPP design used on the late model CR250. However a problem plagued this system. Instead of pivoting the center valve, Suzuki chose to slide it in a passageway of the cylinder. The added mechanical friction made the system prone to binding in one position, half-open. This causes the engine to run flat. Another problem was the shape of the valve. The leading edge that faced the piston was too square and sharp. Even when the valve was in the full open position it caused a shock wave that impeded the outgoing exhaust flow. Grinding the edge smooth reduced the low-end power but helped improve top end. In 1997 Suzuki redesigned the center valve, choosing steel as a material and splitting the valve into two sections, a major and minor valve. They also added a two-stage spring system. With some simple grinding to match the valve to the exhaust port when fully open, this set up was a winner! Suzuki chose to redesign the system in 1998-2000 to the 1997 design. The thought was that the steel valve damaged the valve pocket in the cylinder. Although simply extending the nickel silicon carbide bore material into the valve pocket would've solved this problem.