Engine refused to run on petrol

[pandp38]

Had a scarey moment . I intentionally ran out of lpg whilst measuring the range of tankfull of gas.
Sod's law the tank emptied just as I pulled onto a busy roundabout.
I flicked the switch straight on to petrol but it would not fire up..so had to limp off roundabout.
I took petrol supply pipe to mechanical pump off and was surprised to see it was dry..also filter near tank was clean but almost empty.
Disconnected supply pipe from tank and just got dribble of petrol coming out...removed filler cap thinking airlock/vacuum but felt no pressure.
Spent 10mins debating whether to phone recovery then took pipe off tank again and petrol flowed out this time.
Put pipe back on and after cranking engine over for a few seconds it fired up and drove fine.. done 50 miles today with no problem!

Anyone got any ideas how this could happen?
Thanks P

[ghost123uk]

Had a scarey moment . I intentionally ran out of lpg whilst measuring the range of tankfull of gas.
Sod's law the tank emptied just as I pulled onto a busy roundabout.

Typical

I took petrol supply pipe to mechanical pump off and was surprised to see it was dry..

That is not unusual because there is an electrically operated valve that cuts off the petrol to the pump when on LPG.

also filter near tank was clean but almost empty.

That is normal and an oft misunderstood thing. If you think about it, imagine you have just fitted a new filter. They are fitted on their side of course. Now imagine it starts to fill up with fuel. As soon as the level covers the outlet pipe, fuel starts to flow out of the filter but there is nowhere for tthe air trapped in the upper part of the filter to go, so it always looks like it has loads of air in it, which it has. Of course if you fitted the filter vertically, with the feed from the tank at the bottom, as it filled up the incoming fuel would push the air out of the top and you would then have a filter full to the brim with fuel and no air. As said though, it's normal and doesn't matter.

Disconnected supply pipe from tank and just got dribble of petrol coming out...removed filler cap thinking airlock/vacuum but felt no pressure [you meant vacuum of course ]. Spent 10mins debating whether to phone recovery then took pipe off tank again and petrol flowed out this time.

Now that bit is indeed odd. I don't think I can give an explanation I mean if it was muck in the tank strainer, it wouldn't have fixed itself, won't be an airlock as the pipe runs straight out of the tank..............

Put pipe back on and after cranking engine over for a few seconds it fired up and drove fine

Well that is good news and means you have either a good mechanical pump, or have fitted an electric one. Often the mechanical pump can take quite a while to get the fuel to the carb after not being used for a while. Sometimes so long the battery gives up before the fuel gets to the engine.

Someone else very recently posted on here reminding us LPG users to switch to petrol every so often, just to check everything is working and to keep carb and pump seals and gaskets moist. I tend to use petrol for a short period at least every fortnight (usually to drive to the LPG station after I run out of LPG )

[itchyfeet]

If the tank is low petrol won't come out.

lpg cutoff valve for petrol is after pump on my van ......but if petrol drains down because of a pinhole air leak, there will be no petrol in pipe.

[ghost123uk]

Aside =

lpg cutoff valve for petrol is after pump on my van

I wonder what the most common "Campershack / Gasure" way is. Mine is before the pump. I suppose after the pump at least keeps the pump "wet" with no downside I can think of.

[marlinowner]

If the cutoff valve is after the pump and the hose between the pump and valve fails, petrol will go everywhere and the engine will carry on happily on LPG...

[pandp38]

Thanks for the replies.. just a bit more info:-
I know petrol tank was almost half full as I put some in day before , and also switch between lpg and petrol every week or so.
Seems very odd !

[ajsimmo]

Aside =

lpg cutoff valve for petrol is after pump on my van

I wonder what the most common "Campershack / Gasure" way is. Mine is before the pump. I suppose after the pump at least keeps the pump "wet" with no downside I can think of.

After pump is my norm. As you say, keeps pump wet.

[what2do]

I thought the valves were fail safe, ie. to open, they need to be energised.....is this so?

[ajsimmo]

Ýes, thats right. Or turned on manually with the override valve built into the shut-off valve. That is designed to get you home if electrics fail

[itchyfeet]

If the cutoff valve is after the pump and the hose between the pump and valve fails, petrol will go everywhere and the engine will carry on happily on LPG...

A good point I hadn't thought of.