Lotus Elan

DCOE: Fuel Lines

PostPost by: TBG » Fri Jun 10, 2022 7:19 pm

Can someone please elucidate why one needs a pressure regulator at all. I don't have one and at over 200k have never needed one - or have I? I am confused of West camel!! D
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PostPost by: rgh0 » Fri Jun 10, 2022 9:35 pm

The level in the float bowl varies with fuel pressure as the float needs a higher level to close off the valve against more pressure. A more constant fuel pressure and thus fuel level achieves a more constant air fuel ratio within the limits achievable by the carb tuning.

With the fuel pump / regulator in the boot the approx +/- 1 to 1.5 psi variation you will see at the carbs due to car acceleration and braking is not insignificant especially if sustained for any period and not just a brief transient

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PostPost by: Andy8421 » Sat Jun 11, 2022 5:35 am

TBG wrote:Can someone please elucidate why one needs a pressure regulator at all. I don't have one and at over 200k have never needed one - or have I? I am confused of West camel!! D

Those old Ford engineers were pretty smart. The original engine mounted fuel pump delivers fuel at a regulated pressure right underneath the carbs and avoids the problems discussed in this thread. So, for 200k miles, that little return spring in the pump has been regulating your fuel pressure without you even realising it.

The problems come when you put a pump in the boot, and charge around in the car like Rohan. If you want to go down that route, mounting a pressure regulator near the carbs is an effective solution.
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PostPost by: TBG » Sat Jun 11, 2022 7:46 am

Ah! Thank you - I do have the engine mounted mechanical pump. D
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PostPost by: 661 » Sat Jun 11, 2022 9:42 am

nmauduit wrote:what I meant is as long as the pressure does not go down to 0 for some time (to be defined) there should always be the proper fuel level in a well operating carb (i.e. you may set your warning to 1psi if it gets annoying)

That's a reasonable suggestion. I think I'll do that. It hasn't been on my agenda as many other tweaks are underway.....
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PostPost by: 2cams70 » Sun Jun 12, 2022 12:05 am

If you want an interesting carburettor design to study have a look at the one used on your typical brush cutter. No fuel pump required, operates in any position and not affected by g-forces! The design is derived from carburettors developed for aircraft.
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PostPost by: lance54 » Mon Jun 13, 2022 5:10 pm

Lots of good information here.

I always go for keep it simple and safe on a racecar.

Use a AN bulkhead fitting on the firewall.

Short hose to a AN bulkhead T fitting bracketed to the top of the footwell.

Two hoses from the T to each DCOE from under.

Use AN to metric fittings on the DCOEs.

I think the tube type 90 degree AN fittings are just more elegant.

Put the pressure regulator and filter (if used) in the cabin or trunk to keep the engine bay neat and tidy.

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PostPost by: 661 » Mon Jun 13, 2022 5:15 pm

Personally I think it best to not have any junctions within the cabin, or indeed the bulkhead. Maybe over cautious, but there you have it. I think the bulkhead fittings look quite neat , though
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