Fuel vaporisation problem

[flatcat]

It appears that I finally figured out what the problem with my P6 cutting actually is - as mentioned here before my initial thoughts were the autobox being on the way out.

As I had to get some other work done anyway I asked Ely Services to have a look at the gearbox. They didn't really find anything wrong withit apart from the fact that the fluid wanted changing although I vaguely remembered paying someone else to do exactly that a year ago. Oh, nevermind.

The car was running a lot better on the way back but as soon as we hit the heavy London traffic it was playing up again - although this time it was pretty obvious that is was a fuelling problem.

So, I was thinking of making the following alterations in the hope to finally knock this problem on the head:

- Replace the original engine-driven fan with a thermostat-controlled, suitably powerful electric fan (Kenlowe?). Please note that I don't really want to go dual mechanical/electric fan here.
- Fit an electric fuel pump as per 3500S
- Try to use some of that 'exhaust wrap' stuff to keep the under-bonnet temperature lower or use some fuel line insulation as you find it on some more modern cars.

Does anyone have any additional suggestion or comments on the above?

Thanks,
flatcat

 

[zebedee37]

Electric pump cured mine

 

[PeterB76]

Kenlowe fan shouldn't really be needed. First make sure the cooling system is absolutely top-notch.

Forget about the exhaust wrap, its only really effective on tubular exhaust manifolds that run hotter than cast ones by design. It wouldn't fit well enough to do anything on the standard manifolds anyway.

Before the expense of an electric fuel pump try your idea of lagging the fuel pipes around the engine with heatproof pipe wrap, such products are available from Demon Tweeks and the like. (see their catalogue). And/or moving them from 'hot-spots' as described in the latest P6 News.

 

[Rovertron]

I had exactly the same problem last summer, more than 5 minutes in traffic and the engine temp would start to rise and the fuel would starve. Yet on the move, business as usual.

I fitted a Kenlowe as the temperatures were a bit extreme last summer as a secondary measure thinking it was simply not cooling well in that kind of heat.

However, the car broke down eventually and refused to restart. The chap came out, the fuel pump as too hot and poured water on it (There is a lot to be said for keeping 5 litres of H20 in the boot) Hey presto, it started.

I sourced it to a faulty fuel pump diaphragm that resulted in not a lot of fuel travelling through the system to the carbs and hence evapourating in-situ.

Rather than get a repair kit, I got a good exchange price on a reconditioned mechanical pump with a reasonable warranty. Fitting was fairly straightforward. Last month when it was in for some garage work, my mechanic took it out and recommended switching the thermostat down a bit on the Kenlowe and disabling the mechanical fan.

 

[timj]

Before you go to the expense of a new pump, check a few other things first. I had the same problems as you last summer, and it just kept getting worse and worse.

I replaced the manual pump with a little electric one in the engine bay from Facet. Recommended by Wadhams. This was fine for a bit, but soon the car started running out of petrol on hills. First very steep ones then shallower and shallower.

Got sick of the car for a bit and had a play. Ended up replacing all the fuel lines with copper ones. Bypassing the reserve valve, (It was knackered) and mounting a bigger fuel pump under the boot.

After lying under the car in the rain I was miffed to find that the fuel line from the fuel filter to the first carb under the bonnet was letting in air. It hardly weeped petrol at all.

I just wonder whether this was the problem all along!!

 

[malreid]

@timj has the right idea.

Had the same problem with my S and got caught out a couple of times in traffic, which did not impress me at all. Fixed by installing an electrical pump just behind the rear suspension/diff subframe and running steel fuel lines to the front of the car. Protected the pump from stones etc by using an old mudflap.

Ran a switched electrical supply through a fused relay mounted in the drivers side glovebox using a spare auxiliary feed in the existing wiring loom (I'm not sure what is was for, heated windows possibly). So acts as a cheap kill switch too.

Only disadvantage is not having a fuel reserve.

 

[Rumblin_Ron]

Hi all

There is another thread on the chatroom about this evergreen problem. The conclusion then was that when new the mechanical pump has enough throughput to "overfeed" the SU carbs, the excess going back to the tank down the fuel return pipe. This constant recirculation of petrol meant it never hung arround long enough to vaporize. After 30 years the original pump is getting knackered !

So my advice is that everyones right, assuming there are no blockages in pipes and filters, get a new fuel pump. If this means renewing the mechanicle on (as Rovertron suggested) or an electrical one is up to you. Personally I would renew the valve's on the existing mechanicle pump (see Waddhams and other suppliers, even Lucas ?). You get to keep the fuel reserve, there's no wiring and its as original. Remember even a "high capacity" pump can't force petrol down a SU's throat !

As an aside, it has occured to me that the big mechanicle fan wafting away at all time's probabaly keep things cool with a good flow of air when the car is standing still, just a thought. I used heat bandage on my manifolds, and everything is definatly cooler under the bonnet, whether this help's anything I ca'nt say. .