It's the flightworks pump. There ought not to be any foreign matter in the pump, the BVM UAT bag should have filtered out anything that remains in the fuel. The system from UAT through the pump to the engine is never drained so it ought to have fresh kerosene in the pump, not just oil to gum up or go thick in the cold temps. I wonder now if a lot of the failed starts I have are due to the pump sticking rather than my assumption of low gas pressure due to our low temperatures. I normally don't use the GDT but I will from now on to monitor the temp and see if it fails to start when the temp is okay for the pump to be running.

H