Fuel union on P2

[luli]

Congratulations! It feels good to solve a problem.
On one car I am using AUA25EN by SU. It is a low pessure pump located in the engine bay (for a positive ground car you need AUA25EP). It works perfectly. On the other car I am using Facet cube pump http://www.facet-purolator.com/cube-fuel-pumps.php . This is a high-pressure pump, located near and below the fuel tank. It eliminates vapour locks and costs half the price of the SU. I am using a pressure regulator before the carburetor to avoid flooding.

[RobHomewood]

Set off for 100 mile test run today using the mech pump only. Started OK but near the top of the first long hill there was some fading and some mild backfires. After I stopped for a break she wouldn’t start again. OK I thought that’s vapourisation. I waited for the engine to cool and she started OK (with a bit of priming) However by the return run she was running rough – felt like a rythmic misfiring especially noticeable up hills with a definite surge when the engine kicked in. Is that also vaporisation causing that? The mech pump fuel line runs in the original position on the exhaust side of the car. It was a warm day and the hills did get the temperature up (80 or 90). The gauge did reach the top of the scale at one point in a traffic jam on a hill, with a puff of steam escaping shortly afterwards but the radiator didn’t need topping up. If I ignored the vapourisation possibility I might suspect an electrical fault but all the plugs seem to be firing OK. That leaves the carb and the coil under suspicion. 16.6 mpg approx
Thanks for the info on the pumps Luli- I am looking into that too.

[chris dancey]

I used a pump for an MG Midget with good effect, its dual polarity also.

[dhbuchanan]

Having encountered several problems over the years with fuel supply and fuel vaporisation in P2s, I have followed this correspondence with interest and wish I had been given the following advice a long time ago:

1. Mechanical fuel pumps and the heat conditions which have developed in P2 engine bays since the ill-advised introduction of unleaded petrol are basically incompatible, at least in the case of six-cylinder engines. Unless you actually enjoy hand-priming the mechanical pump when re-starting after every hot stop of more than 10 minutes' duration in summer, blank it off and fit an electric pump.

2. A "pusher" electric pump mounted on the side chassis rail below the RH rear seat is preferable to a "puller" on the bulkhead because it's a lot cooler near the fuel tank. A solid-state cube Facet with a steel filter union attached does a good job at very reasonable cost, but remember that it won't last for ever. Have a spare ready for the first sign of failure. A Facet pumping at 2.5 - 3.5 p.s.i. will satisfy the heaviest engine fuel demand and won't need a pressure regulator at the carb. end of the line.

3. Copper fuel piping in the engine bay should be replaced by a rubber fuel pipe attached directly to the Flexolite at the end of the main fuel supply line and routed up the RH engine bay wall, as far away as possible from the exhaust manifold.

[luli]

Solex 30FAI carburetor is designed for 1.5 psi petrol pressure, therefor a pressure regulator is required when using a facet cube pump. Perhaps SU carburetors can live with a higher value.

[RobHomewood]

Two people today have said the pump located at the tank is preferable to keep it cool. I take the point and will think about it. I am going to replace the pump in the engine compartment with a cheapo (£10) temprarily which will fit without adaptations so that I can confirm that this resolves the problem. Then I shall consider whether to get a £100 SU pump and adapt the pipework or a Facet type and adapt the pipework at the tank more fundamentally. Mike Evans told me he fitted a facet pump with the mechanical one in series on the same line and switched it on when he needed extra power! I hadn't thought of that but instinct makes me wary. In the meantime the kit for rejuvenating the old mech pump has arrived and hopefully that will get put in tomorrow

[dhbuchanan]

SU carbs. certainly can live with a higher fuel pump pressure value than the Solex 30 FAI. The original Solex in my car was ditched by the then owner more than 40 years ago, when it reportedly returned 11 m.p.g., and was replaced by the SU which is still in place. I thought of converting back to the original set-up 25 years ago, but was persuaded otherwise by a number of warnings about the tendency to blockages in the jets of Solex carbs. The SU has never blocked during my ownership.

[Phil - Nottingham]

I fully agree with Howard's first post about modern fuels and his solution.

I on our 1939 16 I fitted a puller SU in the engine compartment (only because I had one spare) some years ago in series with the mechanical one and with switchable to cure annoying vapor lock in traffic (even winter!) but especially after standing with engine off for less than 1/4 hour - manual priming had no effect at all till the allotted time had passed.

This cured it for a year or so and perhaps the petrol formula changed again but it began to be troublesome even after I had the head rebuilt as unleaded with modified waterways to totally cure localized boiling around nos 5 & 6 exhaust valves (causing forceful rad overflow on the overrun sometimes). Perhaps the pump was wearing too but I had no trouble otherwise ever.

I finally bypassed and removed the mechanical pump which has virtually cured the problem but I get the occasional splutter on start up with a hot engine after standing a few minutes but soon starts and runs normally. Most of the pipe is rubber now in the engine compartment but some copper remains and this really does soon attract the heat so I may well remove all this too. Being a 39 it has the less troublesome SU but the carb does soon getvery hot when engine is stopped after a good run.

I think the best place for the pump would be under the rear seat but even though I can switch off the hearing aid I now need I am worried I may hear it clicking which I cannot with the engine mounted pump on the inner wing just below the side panel.

[dhbuchanan]

Like Phil, I sometimes have trouble hearing the electric pump ticking. What I have noticed is that the needle of the dash fuel gauge jiggles about a bit in sympathy with the pulses of the pump when the ignition is turned on, thus providing a visual indication that all is well with the fuel supply.

A significant reduction in underbonnet heat can now be achieved by having the exhaust manifold ceramic-coated by Zircotek. Since having this done last close season, I'd say that their claim of a 33% reduction in heat emitted by the coated engine component is fully justified. I now no longer have to open the bonnet on stopping unless the weather is extremely hot. For a belt and braces job, Zircotek can also coat the exhaust downpipe, but I have not gone that far.

[dhbuchanan]

Re-reading Phil's last posting, I see that I have misunderstood his point about noise made by electric pumps. It was the bit about a hearing aid that led me astray! I take the point that the ticking of a pump under the rear seat might well be more audible in a closed saloon than in an open car like mine. However, the floor carpet and underfelt, both of which should extend up the vertical part of the rear seat mounting, the seat cushion itself and the thick felt which should be in place lining the top surface of the detachable metal seat pan cover ought to be enough in combination effectively to muffle the ticking sound, and certainly so if the driver has any degree of hearing loss.
I mounted my pump on a wooden block fixed in the cavity of the chassis rail in order to minimise sound transmission through metal, and it worked.