That's exactly what mine did until I sorted the wiring out. In fact, my RPM 'spike' was so fast I could hardly see it on the Monitor.

I'd go through start-up - starter would engage, revs build, Propane would go 'pop'...then theeeeeeeeeewwwwwww... die in the bum...

Each time it would do that, it would be pumping a little more Kero into the tube if it got as far as the fuel-pump cutting in for a second or so. Occasionally, it would just manage to get past that and the Propane would actually light the flooded Kero and I would get great plumes of Orange flame out the back as it spooled back down from an aborted wet-start (whereas Propane on it's own gives you a clean blueish flame).

Does that sorta sound like what you're seeing?

BJ