EF Ghia 5.0- stock apart from exhaust- 68 l's LPG 430km's, and thats with a couple a flattenings!! mostly highway tho..

I would firstly run a diagnostic check on your car to see if there are any obvious faults. If that comes all clear, then take it for a run and take your 1/4 socket set with a 3/8 socket for your dizzy clamp. Bump up your timing until it starts to ping and then back it off a bit. You may have to do this a few times. If you have a clean engine(when you can see the graduations on your harmonic balancer), you can do the base timing whilst in diagnostic mode or whatever its called.

Your car should be getting at least 450km around Canberra. My V8 wagon gets 500km and its been mildly worked over so 450km is not unreasonable. So long as your idle mixture and o2 sensors are OK, these things will tune themselves. I would also invest in a new set of leads and some plugs and gap them between 0.75-1.0mm.

Also, the R90E has the balance line to the diaphram, does yours have a tube/pipe/hose that runs from your convertor to your airbox or somewhere where it gets air flowing into it?