I am going to state a few things that are obvious to many of us,
but might be helpful to those that haven't visualized the problem.
As has been established in above posts,
only every other TDC is a power stroke.
(Top Dead Center of the piston stroke)
And due to Hydrogen having the property of
being the fastest flame propagation gas of all.
You don't need to start the "Fire" before TDC,
like you do with much slower hydrocarbon fuels.
Basically what you need is a 2:1 reduction ratio
in relation to the crankshaft's current orientation.
I pointed out the obvious data pickup point above,
with the intake valve being the focus of course.
But that was to use the wire off of any magneto
that is used to stop the engine when done using it.
As the intake valve is in motion at the required time,
I chose that as a fast and dirty "Fix" for all to use.
But the correct way is to get the proper timing information,
and have that be adjustable (To a fine degree) as well.
But anything that has a 2:1 reduction will do.
From the cam gear onward, all things are half speed.
A magnet epoxied on the cam gear edge,
and a "Hall Effect" sensor stationary mounted,
with the circuit from PDF #10 above works too.
Both can handle the oily environment and the heat
if proper parts are selected (Google "Curie Point").
Or an external 2:1 gearset like the "Anton" idea:
http://www.overunity.com/index.php?action=dlattach;topic=9099.0;attach=44176;imageThe Hall Effect sensor is on the stick bottom,
the magnet in that larger plastic 2:1 wheel.
The simplicity of adjustability,
is hampered by many failure points.
I know we live in a day and age of electronic ignition,
But I'm an ancient oldie that believes in points and cap.
An many here may not be electronically inclined too.
So a good-ole set of points and a capacitor instead,
and a trigger bump on the larger wheel for the points.
Might be well within the grasp of all reading here,
considering common home tools, basic knowledge,
and of course, HomeDepot/Lowes hardware selections.
A bump or divot on the cam gear,
a small hole through the crankcase,
and a follower pin to "Points" outside.
That's my vote instead though...