MOPED ARMY

Plug looks good - I usually go for a bit richer but you certainly are not in a danger zone for lean.

Sudden death makes me think you are having condenser issues. On the internal HT coil Mobys you can drill a small hole beside the accessory terminal (look on the back of the genny there is even a mark where to drill) and run a wire from the points out the hole to an external condenser mounted to the right side intake stud. Disconnect the original condenser. Clean the points with a points file (or metal finger nail file) and rinse with brake cleaner (or alcohol).

It is normal to have air in the filter.

When the engine dies out on you does it abruptly stop or sort of die slowly?

Did you check for spark when it dies? If it is a internal HT coil it could be the little spring between the coil and wire that needs to be cleaned or sometimes restretched a bit because that is the contact from coil to wire.

Sudden death = ignition issues.

If you replaced the stock condenser with an external one it might be a bad condenser (it happens)

Or if you left the old one connected (too many people will prompt others to leave it connected by stating "I never had a problem")

Check if the spring is goodly where the plug wire goes into the genny if you have the internal HT coil. You need to ensure all of those contact surfaces in there are very clean.

The darn antiparasite spark plug cap could have a resistor which has finally given up after all these years.

Check inside the genny to make sure you have no wayward wires getting close to the flywheel or cam which could have rubbed through the insulation and are shorting intermittently.

Any time you have issues with ignition it is a good idea to check the index of the points 0,35 - 0,40mm (.013-.016inch) and reset the timing 1,5mm-2,0mm BTDC.

Also always reclean the points with a point file (or metal finger nail file) and flush with brake cleaner (or alcohol), never use sand paper and carb cleaner.

Check the gap in the plug is 0,42mm (.017 inch)