gas question

got a 3.5 EFI lump in a range rover classic, i ahve posted before about a fueling problem regarding petrol but now we are trying to see if we can get it to start on tha gas.
its on a single point via air flow and the system is call...
tartarini
g79sems
appgdmNo 47021gpl
as far as we can gather there is goin to be a switch somwhere that changes it from petrol @2k revs over onto gas,
is there someway of by passin the switch to get it to start on gas? if so where and how?

God knows but my 3.9's switch is on the dash and we run gas nearly all the time, god bless it

this runs on gas all the time aswell but starts on petrol until you rev it then it flicks over