Car drives fine in LPG but is really sluggish on fuel...

[deXtrous]

Idles really low on fuel and commonly stalls. Does not build any sort of speed while revs are going up compared to LPG..

Any reason for this?

I've recently changed my fuel pump and fuel filter.

[Vxceptional]

Could be a number of reasons:

Clogged fuel line
Fuel Injectors stuffed
Dirt
something electrical etc...

Also check to see that the fuel filter isn't leaking fuel and is installed properly (could even be a dodgy fuel filter)

Do a codes test see if anything comes up

[deXtrous]

Isn't there some kind of mechanism that regulated the amount of of fuel that stablises the idle at 900 (or whatever its meant to be). I think that part could be faulty/broken. Unless those are the injectors going straight from the fuel rail that I'm talking about?

I just thought maybe there's be a little tweak I could do to get it up and idling properly again, as it was a pretty sudden fault.