RG500 Power Valve Diagnostics

Symptoms of Malfunctioning AEC:

  1. Symptom: The bike runs perfectly normal up to 8000rpm, where it flattens out. As revs increase to redline, power stays flat.
    • Cause: Power valve stays in open (low rpm) position, and does not close at 7500rpm
  2. Symptom: The bike seems OK down low, but stumbles badly from 5500-7000rpm. All clean by 7500rpm and runs great to redline.
    • Cause: Power valve stays in closed (high rpm) position at all times.
  3. Symptom: The bike runs adequately but not sharp below 7500rpm. Mimics a tired plug or two. Runs great on top.
    • Cause: One or more PVs are installed 180 degrees out of phase, causing the lip of the valve opening to protrude into the roof of the exhaust port, creating turbulence. This stops when the valve closes.
    • Cause: The positive stop cap on #4 cyl PV is installed upside-down, causing the valves to come to rest partially closed when in the low rpm position.
  4. Symptom: The bike has lackluster throttle response, and does not run very well anywhere. Top end is weak.
    • Cause: PV system is non-functional and has come to rest in half open position.

AEC Setup

Let's assume a few things first.
The bike's together, in running order, with the lowers and belly pan removed. So you want to know the operational status of your Automatic Exhaust Control system, eh? Start the motor. From the right side of the bike, operate the throttle while shining a light under the gas tank onto the Power Valve servo motor (follow the PV cables up to the servo location) and observe the cable pulley on the servo. The mark (cast-in line) on the pulley should be at 0 degrees, or straight up when the revs are anywhere below 7500rpm. As you bring the revs up past 7500rpm, the pulley should snap 100 degrees clockwise, closing the valves. When the revs drop back down below 7500rpm, the pulley should return to 0 degrees promptly. If this is happening as described, then all PV related electronics are fine. If not, check for any loose connections with the servo motor or the AEC control unit (gold box located under the taillight attached to the rear fender). If the servo pulley moves at all, your connections are fine. If nothing appears to move, pull up on the PV cable housing #1, located at #4 cyl. If you feel a tug on the cable housing when taking the revs beyond 7500rpm, then something is binding in the valve area or the cables are installed wrong. Check to see that each cable is in good condition and routed correctly; i.e. #s 1-4 on the servo motor matched with #s 1-4 on the PV housings. If you still get no motion at the cable, check the condition and age of the battery. An old, worn out battery will inhibit proper PV function. If the battery is sound, you may need a new servo motor assy. A common malfunction in the servo concerns a micro volt coil which signals valve position to the control unit. When these fail, the servo motor must be replaced. (Note: Testing the servo motor with DC voltage from the battery will not show the problem. The coil is very delicate and be damaged by powering it up with any power source. It is triggered by a magnet connected to the servo drive gear rotating past the coil, exciting it to send it's signal). The AEC control unit is very reliable and not prone to failure.
To check for proper orientation of the power valve in the cylinder, remove the rear PV end caps and slide the valve out, exposing the slot in the valve. Look for a raised notch on one wall of the slot in the valve. The valve should be positioned with the opening at the top and bottom and the raised notch located to the piston side. This is the standard open (low rpm) position. Minor carbon buildup in this area is not a concern since the valve alters exhaust resonance and not flow. On the front cyls. remove the lower pipes to access the exhaust port. Insert your finger into the roof of the port and into the PV slot. The notch can be felt on the piston side of the valve. If one or both valves are out of phase, they can be corrected by partially removing the #2 cyl valve and rotating either one accordingly. Some common causes for sticking PVs are:
  • Cyl head bolts (6mm) are too long due to excessive head milling or the incorrect bolt installed (stock bolts are 20mm in length) and are touching the PV.
  • PV slot has been deformed by placing a screwdriver or some such in the slot to hold the valve to turn the pulley bolt, denting the valve out of round.
  • PV cap installed without a gasket. Without the gasket in place, the cap goes in too far and binds the PV.
Keep in mind that if only one of the PVs is stuck, the whole system jams.

Power Valve Cable Adjustment

Verify that all cables are routed correctly. Remove the #s 2&4 PV housing covers and re-install one screw in each housing. Rotate the PV servo pulley to 0 degrees (straight up). Adjust each PV cable to align the cast in mark on the pulley with the notch in the PV housing. Allow for 1mm of play in the cables and cinch down the lock nuts on the cables. Install the rear PV cover with the raised stop on the pulley engaging the cover between the two bumpers. These bumper stops are positioned in the cap so that there is over 180 degrees of rotational room on one side of the cap and only 120 degrees available on the other side. Install the cap where the raised pulley stop engages the cap within the 120 degree area of the cap. Rotate the PV system by turning the servo pulley or the front PV pulley. Each location should rotate 100dg and return to straight up on the servo and mark to notch on the PV. Install the front cap and go shred!