After re-reading the manuals .....

Jetcat kero versions during the start sequence are useing the Old propane valve
in line with the kero/burner igniter unit to
pulse inject the fuel in order to widen the "stoich point" for ignition. (dripping fuel not a stream)

After ignition it just slowly increases the fuel flow to get to idle.
Hence all that solenoid clicking on start.

On the propane versions, there was an ECU setting to increase the propane flow (solenoid clicking)
if you wanted more flow you adjusted the ecu setting for propane.... less clicking, more flow.
If you wanted less flow the valve opened and closed faster...hence even more clicking.

It seems there are two things regulating fuel flow to the burner/igniter....not just pump voltage.

So has anybody tried adjusting the old propane ecu solenoid settings which is now the ...
"new kero/burner solenoid"setting... increasing
the fuel flow to the burner...decreasing the resistance.........without upping the pump voltage?

(I did'nt know they were shipping with "newer batteries" but ... I have to admit the weak battery theory is toast..)

Upping the pump voltage would overcome a "restrictive ecu setting" on the "old propane valve"
now being used as the kero burner igniter valve....assuming no other restrictions are downstream.
This would also explain why upping the pump voltage is working to overcome the valve
resistance with greater pump pressure.

This was great learning....