RG500 Power Valve Diagnostics
Symptoms of Malfunctioning AEC:
- 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
- Cause: Power valve stays in closed (high rpm) position at all times.
- 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.
- Cause: PV system is non-functional and has come to rest in half open position.
AEC SetupLet'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.