Honda EM3500 SX auto choke not closing

Hi Folks:
I have the above generator and this problem is driving me nuts!

I can start it using manual choke, once engine starts running the vacuum choke servo or diaphragm will pull the choke open. When I shut engine off, the choke remains open and the vacuum diaphragm continues to pull on the choke leaving it open.

If I disconnect the vacuum line to the diaphragm, it releases and the choke returns to closed position. Unless I disconnect the line, the vacuum stays applied to the diaphragm even when engine is off.

There is a check valve and an electric switch solenoid in line with the vacuum hose. Both appear to be working okay. If I apply 12 volts to solenoid it 'clicks' and closes, not allowing any flow. Disconnecting power to solenoid it 'clicks' and allows air to pass through it. The check valve also seems to be okay. I can blow through it one way but not the other.

For the choke to come on, there seems to be a need for the applied vacuum to the choke diaphragm to be released or dissipated before the diaphragm will move and allow the choke to return to closed position. This is not happening, in other words the vacuum applied to diaphragm is held constant or never removed preventing the choke from returning to closed position.

Even when this system is functioning properly, I cannot see how the vacuum that's applied to the choke diaphragm can ever be released when the check valve prevents it.

Something has to release the vacuum applied to the choke diaphragm when engine is stopped. What is it? I gotta be missing something here?

Any suggestions would be appreciated.

Thanks very much.

Dave