Lotus Elan

Fuel Pump Pressure

PostPost by: enskr » Sun Feb 14, 2010 9:23 pm

Now that the original type mechanical fuel pumps are virtually unobtainable, the usual sources offer a replacement type pump, which is a bit smaller and has a metal top in place of the original glass bowl.
I fitted one of these and have had a lot of problems with the engine running way too rich, and even after adjusting the (Stromberg) carbs, could not get a sensible mixture. I'm guessing that the delivery pressure is too high, and the carburettor float valves aren't strong enough to block the flow when the correct level is reached.

Has anyone else experienced this problem and got one one of these new pumps to work, or have I just got a dud pump? I don't particularly want to have to fit a regulator as well.

Thanks

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PostPost by: CBUEB1771 » Mon Feb 15, 2010 2:44 am

This is a common problem. I have added an adjustable fuel pressure regulator between the pump and the carburettors with success. I believe the newer pumps stall at about 7 psig. I don't recall what is correct for the Strombergs but Webers don't like a pump that stalls above about 1.5 psig. I am in the US and use a Holley regulator which is readily available here. I believe there are many good choices in the UK, try Burton Power:

http://www.burtonpower.com/Default.aspx

I have had good luck with them.
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PostPost by: dlbarnes1 » Tue Feb 16, 2010 5:03 am

I had a similar problem with a replacement fuel pump. I added an adjustable regulator set at 2 psi for my Strombergs. Note that the Workshop Manual states 1.25-2.5 psi which appears to be either for Webers or Strombergs.
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PostPost by: Elanintheforest » Tue Feb 16, 2010 7:40 am

Kevin, why not repair your old pump? It's usually only the diaphragm that lets go, and it's a very easy fix...once you have the pump off that is!

I share your views about not getting into having to stick extra bits into the system which has become, for whatever reason, not fit for purpose. I must confess that I don't understand why the smaller metal top pump will over-pressure your system. All Ford Kent and Pinto engines cars from about 1970 had these, and certainly my Escort Mexico, which has a 1600 Kent engine with downdraft weber, has this sort of pump and doesn't have any issues at all.

The kits for the glass-bowl pump are available for about ?15. Here's one on eBay:

http://cgi.ebay.co.uk/Triumph-TR-Alvis- ... 2eaac39e47

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PostPost by: ppnelan » Tue Feb 16, 2010 2:44 pm

Is this over-pressure problem anything to do with the spacer (or absence thereof) that fits between pump & engine :?: :idea:

:arrow: Matthew
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PostPost by: peterako » Tue Feb 16, 2010 3:46 pm

ppnelan wrote:Is this over-pressure problem anything to do with the spacer (or absence thereof) that fits between pump & engine :?: :idea:

:arrow: Matthew


I don't think so.

I think the spacer is there (if it's there) to make sure that the pump lever sits correcly on the jackshaft lobe rather than anything else.
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PostPost by: enskr » Tue Feb 16, 2010 7:19 pm

Thanks for all the advice - look like going back to the glass dome pump is the way to go.

It would be nice if the vendors of these so called "replacement" parts warned you that actually its not a replacement part, just one of the many parts you will need in the course of replacing and re-engineering the system...... rant rant.....

I always assumed the plastic spacer was there to provide some thermal insulation to stop the fuel getting too hot - otherwise why not just make the pump mating flange protrude a bit further?

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PostPost by: Robbie693 » Tue Feb 16, 2010 10:03 pm

Having seen this post I had a chat with the parts dept at Paul Matty today while buying some other bits. They have on their wall display the replacement type fuel pump that is fitted to my car and I asked if they were the same pressure delivery as the original types. The man told me that that yes, as far as he knew they were and they were the ones they fitted to cars in the workshop and didn't use any kind of regulator when doing so..

I have however seen two types of all metal pumps; the one I have (and is stocked by Matty's), which has a domed top and one that is supplied by a few others (QED for one) that has a flat top.

Perhaps they are different in terms of pump pressure? Kevin - I'm sure QED would know the spec if this is the type you have.

Cheers

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PostPost by: RichC » Sat Mar 05, 2016 5:46 pm

I'm looking back at this old topic as I've decided to add in a holley regulator .
has anyone done this here for Weber setup?
Currently there's a 6" piece of braided hose i have running from the mechanical pump on the block to a T piece and I'm thinking of getting a straight union for the regulator inlet and inserting it here .... so far so good !
Next , i'm thinking to get 90 degree angled unions for the regulator outlets and fettle around with the current braided hoses to the carbs , hopefully reusing these also .... however I'm reluctant to have the regulator body unattached to anything but the fuel hoses. .. but where to secure it?
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PostPost by: billwill » Sat Mar 05, 2016 6:55 pm

I have a regulator because I now have an electric fuel pump.

The regulator is held by a longish threaded rod to the front dellorto.

You might be able to do something like this.

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