Vapour lock

Phil Robson

Phil Robson

Well-Known Member
Hazel disgraced herself for the umpteenth time last week. We were going up to the North Yorkshire Moors & got just through Thornton-le-Dale without any issues, then she refused to climb the hill :(:

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There was no fuel getting to the filter & I thought it was a fuel pump problem. However after waiting for the AA for about 1 1/2 hours she fired up perfectly & has run fine since. I'm beginning to think that this has been the root of several issues over recent months & am now keen to grasp the nettle.

From reading various forum threads, the biggest win would seem to be an electric pump. There are many types & ways of fitting & I wondered what the current best option is in the opinions of those who have been there before me! Is a 'pushing' pump mounted near the fuel tank best?

(The picture was taken literally round the corner from "Matthewson's" of "Bangers & Cash" fame. It was an extremely hot day for these parts at around 28C).
 
So it's obviously either the pump or vapour lock, so an electric pump would sort it.

I ran a Facet Red Top for a good while and apart from it just stopping one day, it was reliable. It was old to be fair, and I replaced it with another Facet Red Top and it never let me down again.

It wasn't the quietest of things though. The PO had mounted it under the floor under the rear seat, on rubber bobbins. When cruising along listening to the car and the countryside, you could hear it. You will need a pressure regulator if you use this one though, as it will give around 7 PSI, which is a bit high for SU2.

I eventually put it in the boot and that quietened it a fair bit.
 
FWIW I use a Facet 'cube' pump of the highest output mounted at the back pushing, with a Malpassi petrol king regulator and have not had any probs.
 
Here's a link to my old blog detailing the fitment of a Facet Red Top pump. Fitting-an-electronic-fuel-pump
Fitted 11years ago, cured the vaporization and never given a problem since.

I remove the pump fuse to as a quick way of disabling the car; it will start and drive 50meters then die.

Pump
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Regulator
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Gav.
 
Gargo said:
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Same place I put mine, although I used some 8mm copper pipe to plumb it in with.

I put the regulator up behind the power steering reservoir, don't like hot manis and fuel that close together :)

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Phil Robson said:
From reading various forum threads, the biggest win would seem to be an electric pump. There are many types & ways of fitting & I wondered what the current best option is in the opinions of those who have been there before me! Is a 'pushing' pump mounted near the fuel tank best?
Click to expand...

Just thinking I may still have the Facet and the regulator, if you want to make me an offer for them :cool:
 
Electric fuel pumps are either 'long suck, short blow,' or 'short suck, long blow,' types, so what you need depends on where you mount the pump..
also you need to think if you want to keep the fuel reserve facility, and how much re-plumbing of fuel lines you want to do.
I mounted my Facet pump on the inner wing, near the brake servo, taking the feed from the existing reserve tap.
This need a 'long suck, short blow pump,' Facet or supplier will tell you what sort of Facet you need for this.
Good idea to put an in-line filter between the tank and pump.
When I fitted my pump, I got pump and all bits from a Facet agent who supplied pump, filters, pressure reducer and all
Do not want to worry you, but I have had 3 Facet pumps fail on me:-
1 After 2 weeks; replaced foc. by Facet.
2 After 2-3 years. replaced with 'new improved' Facet. Told by Facet 'never had a new type fail on us yet'
3 After 8-10 yrs, last summer. Fitted a new Facet and keeping my fingers crossed.
I believe that it is a good idea to remove the old mech. pump and fit a blanking plate over the hole.
You should also fit a shock cut out in the pump electric feed, so that it stops pumping if you are in an accident.

Differing opinions as to whether you keep the re-circulating fuel lines, as in the original. If you do the pump runs flat out continuously.
I fitted a restrictor in the return line, so fuel flow very slowly... or you can block the return line completely. Thus you get a warning when vapourization is starting, as you cn hear the pump running continuously, trying to pump fumes.
 
Many thanks for your help guys. I’ve been a bit busy this week but will give some thought to your suggestions over the next few days.
 
I had a Facet 'gold top' fail once, suddenly, after perhaps a decade of steady service. I replaced it with the same again, but moved it to the back as in the NADA cars, including repositioning the reserve tap and changing the cable for a longer one. It 'pushes' from just below the tank. Takes a moment to 'prime' the carbs and return hose, then it fires up. The pump can be heard from outside the car, but when the engine comes to life the faint pumping noise is drowned out by the V8 burble! You can fit a foam moulding to enclose the pump body, reducing noise.
 
I modified my original mechanical setup due to vapor lock. used a cube pump (Repco brand electronic - no points) with airline right angles and fuel fittings to give the same separation as Facet pump. I cut the fuel tap mount off the transmission tunnel edge and mounted it onto the pump and ran a long bespoke bicycle cable through with a joiner to the original cable. The pump i mounted in the same position as the air con cars have it on little cotton real mounts.

I found out very quickly that the return line flowed way too much to keep the fuel bowls full at full throttle. I made a pill up in the exit from the fuel bowl which fixed that issue.

When I changed chassis to a later air con car it had the genuine rover setup as per the manual. the pump mounting bracket and rubber cotton reels are available from one of our normal P6 suppliers.

The factory long cable was very difficult to operate so I've removed it and replaced it with a door lock mechanism driven through a lever and bell crank. i have a two position switch on the dash. The door lock solenoid has a clever little device in its circuit (inside it) which lets the motor run till it stalls then switches the circuit the other way so flicking the switch drives the solenoid (motor) till it stops then the circuit is off till you switch it the other way when the same thing happens. Plan is to wire the choke reminder light as a FUEL reminder light from the reserve side of the switch.
 
Mike, that sounds like a very clever set up. Interested in your remark about the return line flowing too much at WOF. By 'pill' do you mean a constriction in the return tube to restrict return flow?
 
My S2 has, at the tank end, which was blocked anyway.
I just use a cube type Facet and do not have the return in use now - 4bbl carb. Used the return when using SU's though.
IIRC the return orifice / restrictor was small, say around 0.020"
 
Make sure you have cooling water flowing through the 'carburettor tower' and back to the radiator. if the outlet from the tower is blocked, then you will still get vapourisation, even with an electric pump. Until I discovered this, I was being driven crazy with vapourisation, despite my facet pump.
Thanks to Chris York and P6 club, I have sorted this out. If the water flow is blocked, you will get vapourisation, Facet or mech pump.
Getting this sorted out was worth more than my P6 Club membership. Such a simple thing to fix, but not obvious to me or other mechanics who tried to fix my vapourisation.
I was on the brink of selling my 3500S as it had become undrivable in UK summers.
 
By pill I meant a restriction. The normal line is smaller but still flows a lot of fuel back to the tank. From memory i used an internal support piece from a nylon hose end piece used for olive connections. it was a temporary test piece that became permanent when it worked. The FACET pumps slow down as the pressure builds so it is fairly easy to know if the hole is too big as the pump goes at near flat chat.

I took some pictures but its on a phone I accidentally dropped into the toilet; its been on strike ever since. new battery coming so I might get them back....
 
Someone mentioned the other day as to whether either HS6 or HIF6 were more susceptible to vapour locking ?
I have run both HS and HIF and not had any issues. When using HS8 the float chambers were actually resting on the rocker covers. Therefore I do not think it is the carbs that give trouble ( assuming the tower coolant is flowing ) I think it is the fuel lines that need careful routing and maybe even insulating to cure the issue.
 
The issue is in the fuel line. The main feed is suction on the mechanical pump and any electric ones in the engine bay. the engine bay heat is enough to boil the fuel especially on a low tank as the return line heats up the fuel in the tank. Electric pump mounted under the tank as per air con cars fixes the problem as fuel is then under pressure so less likely to boil and if it does the bubbles get pushed through by fresh fuel.
 
Thanks for all your replies guys. :)

I'm a bit bamboozled by some of the info, but it looks like I can use a Facet 'Red Top' pump mounted under the fuel tank (or better in the boot?). I will also need a regulator, but would retaining the mechanical pump do the same job & mean I can keep the returns as they are? I will need a cut-out switch too.

Presumably, unless I do some very fancy pipework re-routing I'll lose the reserve supply?
 
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