EV testing
You can also just pinch off the hose at the solenoid and the exaust valves will open at a lower rpm. You can see the tip rise up to the top of hole in the black plastic cover.
If your exaust valves are not working, first check and clean them. The most common failure is a plugged breather port in the exaust valve body or the ports through the cylinder wall. Inspect the bellows for cracks and the springs. If this looks good check the breather hose on the output side of the solenoid for blockage, crimped. Next test the solenoid itself and make sure air can pass through it when it is de-energized.
Hope this helps,
Cheers