Lotus Elan

Fuel Pressure Regulation

PostPost by: david.g.chapman » Thu Jul 16, 2020 6:36 pm

Just thought I would share my experience today... I was having trouble with a hooting fuel regulator, making random hooting noises at idle - really annoying. I could feel the fuel pipe to the regulator vibrating for every hoot!

So I decided to remove the regulator - after all I had a mechanical fuel pump fitted. It was not the low pressure original but a Burton Power replacement of unknown pressure. Let's give it a go.

When I started the engine it ran OK for about a minute, then started to die, finally stalling. I checked the exhaust manifold pipes with an infra red thermometer and cylinder 1 and 2 were not firing. The spark plugs were dry. After scratching my head a bit I refitted the regulator - engine runs fine after a lot of turning over on the starter!!!

More head scratching, then I removed the regulator again - engine dies. Hmmmmm!

It looks like the front Stromberg carb is getting starved of fuel, with the regulator removed!!!

I can only think that the increased pressure pulses are causing the front carb float valve to jam closed somehow, so the carb empties and the engine stalls. Some form of excessive suction?

Does this make sense? Any other ideas? If nothing else it shows you can't take chances with an unknown mechanical pump- just fit a regulator.

Dave Chapman.
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PostPost by: snowyelan » Thu Jul 16, 2020 11:26 pm

Is the regulator acting as a check valve? I believe there's 2 valves in the pump. If the one on the outlet fails then the prime cycle of the pump will pull fuel back from the carb side. The front carb is slightly higher so it will starve first.
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PostPost by: alan.barker » Fri Jul 17, 2020 7:52 am

If you use a "Huco" low pressure Pump you won't need a regulator.
Alan
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PostPost by: david.g.chapman » Fri Jul 17, 2020 3:44 pm

Thanks to both of you for your replies.

The outlet valve failing idea concerned me, so I have just removed the pump and checked it by blowing and sucking. Both valves seem to be ok. The pump is less than a year old and had only done 1000 miles or so.

I have since put the pump back, and when I started the engine the regulator started its owl impersonation again. Selecting a different pressure setting stops it for a few seconds, then it starts up again. When I set it to 1.5psi it stopped hooting, at least for now.This regulator had been working for over 15 years with several fuel pumps, but started its hooting a few weeks ago. I have therefore ordered a replacement regulator of the same type.

The Profuel regulator is a simple affair with a diaphragm biased against a spring. The spring tension is adjusted by the pressure setting knob to give a cutoff valve action at the desired pressure. Although everything looked OK when I took it apart, it could be that the spring has weakened, or that the diaphragm has become more or less stiff over time. Instead of a damped switching response, the regulator is oscillating at the switching point.

I will see when the new regulator is fitted.

As to fitting an electric pump, this is possibly a to do project as there is a fair bit of work involved - cut off switch etc. I have a Moprod electric pump and tried it in the engine compartment - it made a noise like a jackhammer at 100 yards! Maybe this winter with the Huco pump....

Dave.
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PostPost by: p.faurie » Thu Jul 23, 2020 4:55 am

Like Alan said,why do you need a regulator for a low pressure mechanical pump?
Phil
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PostPost by: alan.barker » Thu Jul 23, 2020 7:42 am

If you have a replacement Mechanical Pump (all metal) that was made in India or somewhere they do produce too much pressure . Been there done it.
If it's original type with glass dome no regulator needed.
Alan
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PostPost by: ericbushby » Thu Jul 23, 2020 8:15 am

Dave,
Blowing and sucking only shows thar one valve is working.
If for instance the outlet valve was stuck open the fuel would flow out and back in again at each stroke producing pulses on the fuel line but not pumping.
You can test it better with water and pump it up a transparent tube vertically therefore testing the pressure
( Half a pound per square inch for each foot of head ), and checking for leaks as well.
Best of luck
Eric in Burnley
1967 Type 45
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PostPost by: david.g.chapman » Thu Jul 23, 2020 1:49 pm

Thanks for the additional replies.

Yes, I suppose that blowing and sucking could miss the output valve if it was stuck open. However, the pump also gave a good pulse of fuel when pumping out of an open pipe. So I thought the pump was highly likely to be OK, given its newness and low miles, and ability to flood carbs at the drop of a hat!

Anyway, I tried a new regulator from ebay that looked like my old Profuel one. it lasted about 10 miles until it gave up on trying to regulate, and promptly flooded my front carb again. Luckily I was just pulling into the garage at the time. That regulator is on its was back to the supplier.

I then heard of some horror stories of similar regulators from the far east failing during use. Apparently the diaphragm can be a poor fit and if it pulls loose or ruptures fuel will come out at pump pressure all over your lovely fibreglass.

I do stress that some of them are OK, such as genuine Sytec pumps.

After some more head scratching I ordered a Malpassi Petrol King (I already have a filter) from Burton Power. It arrived next day - today! I have just fitted it and gone for a run. Everything look OK.

Thanks again,

Dave.
Attachments
1 to 5 psi regulator.jpg and
Generic Profuel/Sytec/Chinese Regulators
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