Hello !When this pump is hot, it runs non stop! 
But ...
I had the same problerm with this donkey pump. When it stops, it cools down pretty fast and it is sufficient to generate a drop of condensation stopping the small mechanical shuttle . This is what I think but is it the reason ??!
So to avoid this, I made a hot jacket surrounding the top pump and in which the steam supplying the D10 circulates permanently. Keeping the pump hot. For info, in my case the D10 does not have a reverse but a variable picth propeller. So the steam is always running the engine at 500/600 rpm.
If you look at the photo , I even made a bleed off valve on top to allow the condensate to be blown out and re-starting the pump when necessary .
Unfortunaly , even with this device, if the pump stops , it does not start again, 100% of the time , even when hot.
So I finally let it run permanently through a by-pass valve like Jerry does and I adjust the level in the boiler by adjusting the by pass opening.
Not easy to manage from the shore. Maybe a concession to the new technology like an inboard small camera can help ?
Also, with the usage, it may be very possible to adjust the stroke rate to the steam consomption wich is stable in that case.
Just need time , practice and sun !
Steam with no problem is NO fun!
Cheers!
