Lpg

Hi im new to this forum and i have a series 3 petrol which on petrol is running okish sometimes feels not idling fast enough but then when i go on to LPG will imcrease power then just die. would anyone be able to help me with possible ideas please.

OK.... lets get some perameters in here; presume 2.25 four pot landy engine; presume stock zeneth carb and points ignition; presume open loop mixer LPG system.....
Next up, do you have a gas control module (often combined with LED gas guage) or is it a fully manual switch over...
You say sounds like idle on petrol too low, then .more power' when switched to gas, then dies.....
Do I assume you mean, on the drive at rest, on idle, it idles low on petrol, switch to gas, it picks up (revs increase... more power?) then dies....
OR, that when driving, you switch to gas, motor seems to 'surge' then falters and dies....
Ie dead motor, and coasting to a halt, or if you switch back to petrol it falters and goes again?
Has it ever run right? Is this a new to you car you are 'de-bugging' or is this a fault that has recently developed?
Now, if you are de-bugging a new to you motor, and it has a low rent or DIY conversion that doesn't have a gas control module, or perhaps if it does, but its not a very good one, the 'increase in power' or pick up in revs when you switch over COULD be that its running off the petrol in the flpat bowl, AND adding gas, so going well ritch, like putting the choke on, momenterily, THEN as float bowl empties, there's not enough gas to keep it going....... OR its not switching off the petrol, then as gas comes in, initial 'wiff' gives pick-up like putting choke on, then goes cronic ritch and floods......
But that's leaping ahead.....
First of all, pull the plugs and see what they look like..... if running ritch will be black and sooty.....
Next, investigate your LPG system, and tell us what you got, and see if you can elaborate on the 'symptoms' so we have a bit more to go on....
Are you making sure that the engine is warmed up properly before switching to gas, so the evaporator is actually boiling the LPG, for instance?

its 2.25 four pot landy engine,stock zeneth carb and electronic ignition; presume open loop mixer LPG system
it does have a gas control module
idle is ok on petrol on drive but when go driving it can cut out if revs decrease for example as slow down to stop at lights not always though.
when on the drive it ticking over ok then when i go to change to gas changes over and idles nice speed then will feel little increase inpower beofre dies. it used to run fine but had been sitting on drive for about year and have started to use the car as can drive it now and has only just come about. can sometimes get black soot but rarely do normally white cloud of fumes when change over and when i change over sometiems sounds like splattering when changing over then after second clears.

OK, you've corrected to 'electronic ignition'....elaborate please; OE ignition is points, with mechanical advance.
Electronic ignition could be anything from a fully mapped aftermarket set up, like a Mega-Jolt, to a 'transistorised' points system, that simply gives an amplified low tension signal to the coil, or a 'contactless' system, that keeps the mechanical advance mechanism, but replaces the points with a hall effect pick-up, or an optical 'cutter' mechanism.

As its the more common, I am presuming 'transistorised' points 'electronic' ignition.

You say it drives 'OK' on the road, on petrol, but sometimes 'falters' when slowing to lights, or do you mean when actually stopped at lights?

I'm diagnosing by guesswork and ESP here........ but suspicion I have is ignition related.

FIRST thing though, is to get the old girl running right on petrol..... THEN we can worry about the gas.

Lets start with the basics, if she's been sat, shall we?

1/ remove the spark plugs one at a time; look at the colour of the insulation, and compare it to this: Sparkers Tell-Tales
Next, clean the spark plug thoroughly, gap and insulation, or replace with new.
Set the plug gap to 0.75mm before re-fitting. (Or reccomended gap for LPG)
Get some white spirit or methalated spirit on a rag and clean the spark-plug lead.
Use a little emmery to clean the copper contacts on either end, AND the hole it fits into on the distributor cap, then refit.
Repeat for all spark plugs, doing one at a time, so you dont get the plug leads mixed up.
Then clean the 'king-lead' the fifth, middle HT lead between teh centre terminal on teh distributor and the coil.
2/ Remove the distributor cap; with fine emery or wet and dry, clean the terminal pins, and the brass contact on the rotor arm.
3/ clean the contacts on the points; identify and replace the condenser.
follow instructions in the haynes manual, to set the 'static' timing and points gap.
4/ run the engine up, and adjust idle speed on the carburettor.
5/ Go for a drive, get the car good and warm, and drive it over wide veriety of conditions; Hard acceleration; high-is sustained (two or three minutes) road-speed, PREFERABLY with a forth gear hill in there. Deceleration on 'part throttle' for corners, and full deceleration as for coming to traffic lights, etc.
6/ Return home, allow to cool; remove a spark-plug, compare to chart, and report findings on how she behaved on the road, and what the spark-plug looks like.