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Theo Whitmont
New User
Username: old_mate

Post Number: 36
Registered: 04-2020
Posted on Wednesday, 21 April, 2021 - 16:02:   Edit PostDelete PostView Post/Check IP

Gents (Ive given up on there being any ladies here, but happy to be corrected),

After 18 months of scouring the internet I have finally sourced an Autovac for my 20/25.

I have been keen to rid the Old Girl of the new fangled electric pump that was installed in the 70's, which by the way is very reliable even if a bit over eager to perform its work.

Before I take the leap, I would be appreciative of any comments and thoughts about whether this is a good idea or not. I wonder why it was so popular to pull them out of the car?

Am I asking for trouble or should I let sleeping dogs lie?

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David Gore
Moderator
Username: david_gore

Post Number: 3923
Registered: 04-2003
Posted on Wednesday, 21 April, 2021 - 19:15:   Edit PostDelete PostView Post/Check IP

Hi Theo,

Being a confirmed wearer of a belt and braces "to be sure to be sure"; I suggect you give consideration to a dual fuel feed set up as below:

1. Restore the Autovac in its rightful place with all connections in place and operational. Install a cut-off tap in a hidden place to isolate the Autovac in the event of it having a "hissy fit".

2. Remove the electric pump if it is in a visible location and reinstall it in a suitable location where it is out of sight.

3. Install appropriate pipework between the fuel tank, the electric pump and a hidden connection to the fuel line between the Autovac and the carburettor. I would install a non-return valve between this connection and the discharge connection of the Autovac to prevent backflow when the electric pump is in use.

4. Install the necessary electrical wiring and activation/shutdown master switch in a way that it can only be seen when activation/maintenance is required.

5. You might consider including a pressure relief valve in the electric pump discharge line with the overflow being returned to the fuel tank if over-pressure has been a problem with the existing electric pump system.

This modification would give you the best of both worlds; one being a return of the original fuel system and the second being a reliable back-up should you encounter an embarrassing "failure to proceed".
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Dorien Berteletti
New User
Username: dorien

Post Number: 15
Registered: 01-2013
Posted on Wednesday, 21 April, 2021 - 22:30:   Edit PostDelete PostView Post/Check IP

I've done pretty much what David has suggested.
My electric is mounted in the trunk area and is an SU low pressure..about 3 psi?
The electric gives you peace of mind and particularly useful when the car has been sitting for months and there is not much fuel or none in the Autovac.
Turn on the electric, wait till it stops clicking and you start.
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Theo Whitmont
New User
Username: old_mate

Post Number: 37
Registered: 04-2020
Posted on Wednesday, 21 April, 2021 - 23:39:   Edit PostDelete PostView Post/Check IP

Hi David and Doriien,

I acknowledge this sounds like a great balance between the certainty of modernity and the charm of yesteryear.

I was following this route but was warned off on the basis that if I forgot to turn off the auxiliary pump, I would be in danger of a fire.

See the link to just such an occurrence.

https://www.luxuo.com/motoring/automobile/rolls-royce-phantom-ii-endures-trans-continental-peking-to-paris-rally-with-dato-sia-hok-kiang.html

A possible solution could be a timed switch to account for any lapse of concentration. Could such a thing work?

Thanks in advance for your thoughts.

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Dorien Berteletti
New User
Username: dorien

Post Number: 16
Registered: 01-2013
Posted on Thursday, 22 April, 2021 - 00:35:   Edit PostDelete PostView Post/Check IP

No, don't complicate an easy solution.
Your switch to the electric pump is ALWAYS wired from the ignition switch!!
When you turn off the engine regardless if the pump switch has been turned off, the pump will be off also.
Dorien
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David Gore
Moderator
Username: david_gore

Post Number: 3924
Registered: 04-2003
Posted on Thursday, 22 April, 2021 - 09:12:   Edit PostDelete PostView Post/Check IP

Hi Theo,

Dorien is correct - if you want a "belts and braces" solution to isolating the electric pump completely; it would be a simple exercise for someone with electronics experience to design and specify a device that would also permanently isolate the electric pump circuit as soon as the ignition is turned off and restore power when the ignition is turned on.
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Theo Whitmont
New User
Username: old_mate

Post Number: 38
Registered: 04-2020
Posted on Thursday, 22 April, 2021 - 12:31:   Edit PostDelete PostView Post/Check IP

So having re-read the article - the writer seems to say that the driver turned on the electric pump whilst driving to supplement the autovac which had a leak and was thus unable to meet the demand for fuel.

This lead to an oversupply and spillage that found its way to the manifold and the rest is history.

Does this change anything? I see the method suggested by David & Dorien is designed to resolve a difficult start up.

Would there be any reason to run the auxiliary pump whilst in motion or is that stupidity in action?
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Jeff Martin
Frequent User
Username: jeff_r_1

Post Number: 228
Registered: 07-2018
Posted on Thursday, 22 April, 2021 - 17:13:   Edit PostDelete PostView Post/Check IP

I don't think it would take much to have a valve and solenoid set up to divert the supply of fuel away from the autovac when introducing the auxiliary fuel pump to take over.
For anyone who may find that it's too much bother to get out and shut the fuel supply off from the autovac.

Personally if I had a car with what sounds like a rather temperamental way of getting fuel to the carb(s), I would just have the SU pump on all the time.
The autovac would be in place for show purposes only.
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Mark Herbstreit
Frequent User
Username: mark_herbstreit

Post Number: 220
Registered: 05-2005
Posted on Thursday, 22 April, 2021 - 19:07:   Edit PostDelete PostView Post/Check IP

I have been knocking around in 20/25 GNS60 and P1 56 MC for about a decade. Both autovacs have never given a seconds problem. I have also covered a fair distance in Wraith WRB60 with electric pumps that have failed on more than one occasion.
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Dorien Berteletti
New User
Username: dorien

Post Number: 17
Registered: 01-2013
Posted on Thursday, 22 April, 2021 - 22:46:   Edit PostDelete PostView Post/Check IP

Let's look at common sense.
Electric pumps have been around since the 40s and no issues. In the case of Rolls Royce they replaced the Autovac as a better system.
Pretty much all English cars had them. Haven't seen a postwar MG/Jag/Bentley+++ owner retrofitting an Autovac for greater reliability.
I have a valve, manually operated, so I can bypass the Autovac when I want to.
Given the variance of modern fuels in North America, I tend to run on the electric when in traffic.
I also have a dedicated electric fuel pump that pumps from the reserve line.
In essence I have the option of 3 systems.
Both electric pumps are hidden in the trunk area close to the petrol tank.
Obviously if the Autovac is leaking, given the exhaust is right underneath, the risk of fire is quite high.
Must be a RR feature because on a MkVI the frt carb overflow line feeds on to the dynamo.

Dorien
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ChristopherCarnley
Unregistered guest
Posted From: 159.242.227.81
Posted on Thursday, 22 April, 2021 - 20:10:   Edit PostDelete PostView Post/Check IP

The Autovac can be problematic, and as a pragmatist, I would go with Jeff's suggestion.

A clean sweep with just a double ended, low pressure S.U. electric pump, fitted in front of the fuel tank.
The ones fitted to the Derby Bentley on the bulkhead sound like a pair of machine guns.

(Message approved by david_gore)
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JonasTrachsel
Unregistered guest
Posted From: 85.7.52.221
Posted on Saturday, 24 April, 2021 - 16:50:   Edit PostDelete PostView Post/Check IP

No need for an electric fuel pump to help at starting the engine, even after a long winter lay-up.
When starting the engine of GZU7 for the first time after winter lay-up I turn the engine over with the starter without ignition on, until I see oil pressure on the manometer. Until then the Autovac has had plenty vacuum/time to fill a dried-up float chamber.
A simple non-return valve in the fuel line just where it comes out of the tank keeps the long fuel line to the Autovac filled with fuel all the time and helps to restart also a hot engine.
In defense of the Autovac: I have done approx. 25'000 Miles without the least hicup of the Autovac, but had vapor lock problems before fitting this non-return valve.
Jonas

(Message approved by david_gore)
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JonasTrachsel
Unregistered guest
Posted From: 85.7.52.221
Posted on Sunday, 18 July, 2021 - 22:27:   Edit PostDelete PostView Post/Check IP

In addition to my above post I would like to point your interest to an article published many a moon ago in the RREC Derby Phantom Register Newsletter No 5, page 3. I am not sure this link will work for you, as you must log in to the members' section of the RREC webpage:

file:///C:/Users/jotra/Downloads/Derby-Phantom-Register-No.-05-January-1999.pdf

This article deals with a in-depth research of the dreaded vapour lock situation in some of our cars and finding the solution with the non-return valve I mentioned in my above post.

(Message approved by david_gore)
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Dorien Berteletti
New User
Username: dorien

Post Number: 20
Registered: 01-2013
Posted on Monday, 19 July, 2021 - 23:11:   Edit PostDelete PostView Post/Check IP

Not being a member I can't access the info, however, a solution that "may" work in some parts of the world may not in others.
I don't have issues and I don't have a no return valve. Fuel formulations vary regardless of ethanol, and given that fuel does not jump out of it's container/float bowl, I'm unsure as to what use a no-return valve is.

Dorien
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David Gore
Moderator
Username: david_gore

Post Number: 3964
Registered: 04-2003
Posted on Tuesday, 20 July, 2021 - 09:40:   Edit PostDelete PostView Post/Check IP

Dorien,

The non-return valve does exactly what the description describes; it maintains a constant level of fuel in the line from the fuel tank to the Autovac especially when the car is climbing long grades which could cause the fuel in the line to the engine to flow back to the tank causing fuel starvation leading to engine shutdown or intermittent "stumbling" as a consequence.
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Dorien Berteletti
New User
Username: dorien

Post Number: 21
Registered: 01-2013
Posted on Tuesday, 20 July, 2021 - 23:04:   Edit PostDelete PostView Post/Check IP

I know BUT I've managed for over 50 years without one and at no time have I felt the need for one.
Before me, when these cars were new, the same applied.
I always wondered how "good" was/is the suction from the Autovac ( on some cars) needing this band aid help?

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