Had the exact same problem with my J800R, thought there was something drastically wrong with the turbine or pump or ECU or programming. Turned out to be a small matter of starting technique. I simply shut off the propane as it ramps through 10-15k rpm. It continues to ramp perfectly on kero. My head tells me the ECU and solenoid should be controlling the propane and I should be able to just sit there and watch. Experience tells me too much propane can be a problem, and the small task of shutting off the propane a little early solved the problem. Give it a try and let us know...