Hi guys, needing some help - on my 351 which is on gas, there is a lock off type valve on the petrol line just before the carby. I get that this is necessary to shut off petrol when its on gas, what I fon't get is how its set up. Two wires come out of it, one to earth, fair enough - the other goes to a vaccum switch which is then connected straight to the ignition by the looks - I don't get how it detects whether its on gas or petrol from that...in other words, when and how is that valve getting triggered? Also, gas fitter guys might know this one, is its ` rest ' state , i.e. no power going in, open or closed? If there were no wires connected would it allow petrol flow or stop it? (Can't test it at the moment bewcause I'm about to hook up the petrol to get the dual fuel thing happening but need to do a few things before I can put any petrol through it...) If it helps this is on an old Impco 300 ugly assed hanging over one rocker cover type setup...(see, I know all the technical terms!!)

with power off it should have ALL valves closed on gas side at least

yes, I understand that - but what about the one on the petrol line?

Because we can't physically see your setup, it's a bit hard to advise.

I'd assume all valves need 12v to open - certainly the case for the LPG lock offs.
Surely you can take the petrol one off and test it just to be 100% - shouldn't be hard.

If you have no joy with the petrol setup, with the wiring, what you can do is wire up a 5 pin relay with it's coil powered off the lockoff power (pin 86 lockoff power/pin 85 earth) pin 30 needs IGN 12v - such as off ignition coil power for example, pin 87A goes to the petrol valve.

Should be easy to setup - that's about all you need.
The LPG controller safety side should still work as per - so there's no safety compromise.
The system should default to petrol if there's an LPG issue.

Yeah thanks for that, I had a think about it this morning and I think what they've done is set up the vaccum switch mentioned to trigger when it sees vaccum at the lpg setup, thus shutting off the petrol line. (vaccum line goes to the mixer)

Yeah, sounds a bit clunky.