I have seen and experienced issue you have... The PST 600 on ethier the Tems ECU or xicoy/gaspar fadec will hang on the start and fail to ramp up to idle if the ECU battery is marginal, (I think the PST starter design draws more power than the standard bendix, because of the many one way starter roller bearings) if your using a NIMH ECU battery switch to a NEW Nicad as the Nimh pack might not have the extra amps output to push the engine over the top. Most failed starts on mine were either operator error (on the propane) or the battery.....otherwise its been a gem of a engine.

I concur with stratotanker....Going to manual propane control also helped it over the hump and negated any further long time hanging issues.(external bottle plumbed thru the plane straight to the engine with only the check valve between the engine and Bottle) It takes so little propane to light it off, I removed the pst onboard propane valve from the system.

Don't forget ...NOT TO DO... multiple "Dry starts" as the bearings need to get lubed with some fuel between starts. Running on just the propane burns up the " bearing start lube" and eventually the bearings. The pump test feature can be used to lube the bearings prior to another start.(Any excess fuel in the engine does NOT dump as well out the back as it does the front of the engine....which was a nasty suprise)

Hope this info helps get....."Little blue" running... cool.