bug bear lpg to petrol

Hi All. A bit of a bug bear with my v8 110 3.5 su carbs I think.

  1. I run on petrol normal no problem
  2. I can run on lpg normal no problem
  3. I can switch from petrol to lpg no problem But switching from lpg to petrol it stalls due to lack of fuel I guess. I can hear my electric pump in the fuel tank working. So after continued pump and restarting it eventually get through. Now my guess it to do with being dry system from running on lpg, then having to refill su carbs and pipes then inlets. The only thing I can see preventing is a fuel cut switch. Any advice would help.

regards john live in manchester

Reply to
john oakes
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You'd expect it to run very rich until the float bowls empty, I usually drive with both lpg and petrol off until the engine falters, then switch in the lpg.

I cannot see any way around this with the SU carbs, mind they take only a few seconds to fill.

AJH

Reply to
AJH

Should clear that point I do run the petrol out till my engine stalls then switch to lpg.

That what seem strange it can take upto a minute of me trying to restart. I can hear the difference with accelerator foot down and foot up. I am trying to avoid destroying the starter motor.

john

Reply to
john oakes

my car will go from LPG to petrol perfectly - but i have a mechanical fuel pump and the cut off solenoid is only about 1 inch from the carb

- so i have full petrol pressure right up to the cut off solenoid even when running on LPG.

Im assuming that your stalling is due to the time it takes the fuel to get from the petrol pump to the carb - This would make sense. 101's can be hard to start but if you force the fuel pump on for a few secs before turning the key they catch much quicker.

The only way that i can think of getting round your problem is to see if the LPG controll/switch over can be programmed to, when going LPG-petrol, turn the petrol pump back on a second before the LPG is cut off to allow for the juice to get from the pump to where it should be.

Otherwise - just plan to switch from LPG-Petrol when you are already moving. This is how i go from petrol-LPG as it takes about 30 seconds for the carb to empty even once it has been cut off!. It doesnt matter if it splutters a bit if you are already moving.

Reply to
Tom Woods

Tom Woods uttered summat worrerz funny about:

Tom if you still have the dumb squadie anti engine destruct device fitted then dump it. As in the feed to the fuel pump killed until the oil pressure is up.

Morph is far happier now and as long as you don't run out of oil / oil pressure then theres nowt to be lost.

Lee D

Reply to
Lee_D

Despite being told it's bad practice I have left the pump in the tank running while the ignition is on, so the fuel is at pressure all the way up to the solenoid by the carburetors, hence the carbs fill in seconds and the pump doesn't need to prime or replace any fuel that has settled back to the tank.

It means if the lpg runs out I only lose a few mph in traffic for tens of yards as I switch over, I try to avoid running on the last drops of lpg when in stop start traffic, though I did think up a warning system for low lpg but never implemented it.

AJH

Reply to
AJH

Never had it and its not going back on!

Im going to fit a pressure gauge so i can see what it is doing.

Reply to
Tom Woods

I should clear this part I allow the carbs to run dry before switching to lpg.

That what seems strange in the length of time to refill the carbs.

regards john

Reply to
john oakes

My fuel pump originally was on but because of the pressure this would leak at the cut switch connection. So I had a relay fitted to switch off the petrol.

How long would this take to refill the carbs. Also I tried switch over on the motorway and this struggled for a mile and stalled at a set of lights.

regards john

Reply to
john oakes

It shouldnt leak - that probably isnt helping you either. Try fixing it and leave the fuel pump running all the time.

I'd guess it takes a few seconds.

You could disconnect the fuel pump, run it dry and then try starting it with the fuel pump on a manual switch and see how long it needs before it will run.

Reply to
Tom Woods

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