bug bear lpg to petrol

J

john oakes

Guest

• Aug 28, 2006

• #1

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

 

A

AJH

Guest

• Aug 28, 2006

• #2

On 28 Aug 2006 04:46:19 GMT, john oakes <[email protected]> wrote:

>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

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.

>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.

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

AJH

 

J

john oakes

Guest

• Aug 28, 2006

• #3

In <[email protected]> AJH wrote:
> On 28 Aug 2006 04:46:19 GMT, john oakes <[email protected]> wrote:
>
>>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
>
> 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.
>
Should clear that point I do run the petrol out till my engine stalls
then switch to lpg.

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

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
>
> AJH
>
>

 

T

Tom Woods

Guest

• Aug 28, 2006

• #4

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.

 

L

Lee_D

Guest

• Aug 28, 2006

• #5

Tom Woods <[email protected]> uttered summat worrerz funny
about:
> 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.

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

 

A

AJH

Guest

• Aug 28, 2006

• #6

On 28 Aug 2006 11:58:04 GMT, john oakes <[email protected]> wrote:

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

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

 

T

Tom Woods

Guest

• Aug 28, 2006

• #7

On Mon, 28 Aug 2006 14:10:21 +0100, "Lee_D"
<[email protected]> wrote:

>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.

Never had it and its not going back on!

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

 

J

john oakes

Guest

• Aug 29, 2006

• #8

In <[email protected]> AJH wrote:
> On 28 Aug 2006 04:46:19 GMT, john oakes <[email protected]> wrote:
>
>>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
>
> 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 should clear this part I allow the carbs to run dry before switching
to lpg.


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

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

regards john

 

J

john oakes

Guest

• Aug 29, 2006

• #9

In <[email protected]> Tom Woods wrote:
> 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.

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.
>
> 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.
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

 

T

Tom Woods

Guest

• Aug 29, 2006

• #10

On 29 Aug 2006 02:35:55 GMT, john oakes <[email protected]> wrote:

>In <[email protected]> Tom Woods wrote:
>> 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.
>
>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.

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

>> 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.
>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.

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.