SU fuel pump

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theelanman
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SU fuel pump

Post by theelanman »

the diaphragm in my fuel pump has expired........

anyone know if there's a rebuild kit or do I have to buy new?.......(about £120)

or recon (about £90 from Lotusbits)

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DavidOliver
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Re: SU fuel pump

Post by DavidOliver »

SU UK supply both kits for original points and diaphragm or electronic substitute. Log on to SU for details.
Get ready to empty the tank while fixing and look for fibreglass integrity behind the securing rubber bobbins.
Youtube also shows how to repair, not difficult.

Dave the cog.

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rbgosling
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Re: SU fuel pump

Post by rbgosling »

I replaced my SU pump with an imitation Facet one from eBay. Also had to track down a couple of adaptors to get the right thread to screw to existing pipes, but still WAY cheaper than SU. Worth mounting it with a rubber mount, as it ticks more than an SU, I can’t hear mine over the engine now.
My pump (‘90 Excel) is mounted above the top of the fuel tank, so no need to drain the tank. Other cars may be different...
"Farmer" Richard

1990 Lotus Excel SE (Lilith)
2004 Jaguar X-Type Estate

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The83Boy
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Re: SU fuel pump

Post by The83Boy »

I've recently replaced my Type 83 Elite fuel pump with an Electronic SU type. The old part had AUF305 on the body as the part number, and I was advised by SU (Burlen) the AZX1307(EN) was the current equivalent so that is what I went with. They also offered EPK300 as the repair kit I'd need for the AUF305.

It's all fitted and working now, but for some reason it doesn't stop 'ticking' once the systems primed. When the old pump was working it would operate rapidly when powered up, then slow down and stop as the system pressurised. A couple of pumps of the pedal to prime the carbs before starting and it would tick again once or twice, then stop. If it didn't I'd look for a leak, and usually found a jubilee clip or banjo to nip up and that would sort it.

With the new pump I can't identify any leaks though, so can anybody suggest why that might be? I wonder if it could be a characteristic of the electronic version compared to the mechanical pump, or if perhaps the new unit is operating at a slightly higher pressure and overwhelming the floats. 3.8psi is the max pressure according to the SU website. The only other thing I can think of is that there's some air in the system, but an 80 mile drive last weekend didn't clear it if there is.

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Lotus-e-Clan
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Re: SU fuel pump

Post by Lotus-e-Clan »

I have the SU electronic replacement. I kept the box and it has AZX1308EN on the sticker.

This replacement behaves exactly the same as the original ...it stops ticking when the float chambers are full.

No idea if 1307 is different (or wrong) but the 1308 is certainly the right one AFAIK and have so far found.

I got mine from Lotus Bits BTW.
Peter K

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The83Boy
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Re: SU fuel pump

Post by The83Boy »

Thanks Peter.

According to Moss, the 1307 is a 2.7psi version and the 1308 is a 3.8psi version, although I couldn't find anything to confirm this on the otherwise quite comprehensive Burlen (SU) Website.

If I've got the lower pressure version then it's unlikely to be overwhelmed floats causing the continued pumping. Hmm?!?!? Investigating to be done next time I'm in the garage.

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Lotus-e-Clan
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Re: SU fuel pump

Post by Lotus-e-Clan »

:idea: Just a long-shot.

Depending on what additional filters/valves you have between the pump and the float valve, the final pressure at the carb float valve may not be the full deliverable pump pressure. Valves have 'pop' values. For example, a non return valve might have a 'pop' value of 1 psi (takes 1 psi to keep it open) which means the pump's 2.7 psi will drop to 1.7 psi upstream of the non return valve...which in turn may mean the float valve may not have full/flow/continuous flow, so the pump is playing catch-up?
Peter K

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Re: SU fuel pump

Post by alanmoss »

Lotus-e-Clan wrote:I have the SU electronic replacement. I kept the box and it has AZX1308EN on the sticker.

This replacement behaves exactly the same as the original ...it stops ticking when the float chambers are full.

No idea if 1307 is different (or wrong) but the 1308 is certainly the right one AFAIK and have so far found.

I got mine from Lotus Bits BTW.
1308 is the one on mine.
Alan
Excel Celebration, 1999 Mini Cooper S, Dacia Duster 4x4

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DavidOliver
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Re: SU fuel pump

Post by DavidOliver »

For Lotus-e-Clan. A clarification on pop-valves (non-return)
In my opinion (and I respect your knowledge of our cars) a pop-valve once opened does not reduce pressure upstream. It is open or closed and once open does not restrict flow and therefore does not reduce pressure (OK you lose a little bit).
Discussion please.

Dave the cog.

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Lotus-e-Clan
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Re: SU fuel pump

Post by Lotus-e-Clan »

DavidOliver wrote:For Lotus-e-Clan. A clarification on pop-valves (non-return)
In my opinion (and I respect your knowledge of our cars) a pop-valve once opened does not reduce pressure upstream. It is open or closed and once open does not restrict flow and therefore does not reduce pressure (OK you lose a little bit).
Discussion please.

Dave the cog.
I see where you are coming from Dave. I guess it may depend in the valve design?

My thinking is that if a non-return valve design comprises a concentrically-sprung-in-line lid which needs 1 psi to open it (pop-value), then pump pressure has to continually work to keep it open against the spring continually wanting to close it, thus losing 1 psi in the flow downstream of that valve.
If the valve is a hinged-flap, then I guess you might be right in that if the spring holding it closed has gone over top-dead centre when fully opened, it may not be pressing back with the full pop value in the open state compared to the closed state. Also I guess an extra bit of pressure may be needed to initially 'unstick' the valve flap from its seat, so the pressure needed to keep it open will be a tad less than the pressure required to open it.

Any how, regardless of the multifactorial nature of a valve's 'pop' value, my comments about the pressure loss mainly relate to the research (reading) I did before modifying my Excel's oil pressure system combined with my actual findings on the modified oil system where I have oil pressure sensors pre and post the oil filter (ie two identical VDO pressure sensors read by the same std VDO gague). I also run two oil temp sensors in the same fashion (see below how it is set-up)
Image
Here it's measuring the pressure drop post filter. The differential readings depend on oil temp, but when fully hot, the filter takes away half a bar (7 psi).

In my reading around the topic I found others who had looked into the differences in oil pressure between cartridge filters, also looked into those that have a non-return valve (anti-drain) and those that do not. Their finding were that the anti-drain valve cartridge lost pressure compared to the non-valved cartridge, which was consistent with the manufacturers stated 3 psi 'pop' value for the anti-drain valve (silicon diaphragm type).
So the evidence I've gathered so far indicates that there is a cost for having a non-return valve in the system. From this I assume that the 7 psi loss in my system post filter (when hot) comprises about 3psi loss due to the anti-drain valve and 4 psi due to the resistance in filter matrix.

And from these findings I've assumed (rightly or wrongly) that the same would be true for non-return valves within the fuel system (trying to keep it on topic )
Peter K

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DavidOliver
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Re: SU fuel pump

Post by DavidOliver »

In our fuel line to my knowledge there is no non-return valve, the fuel pump restricts back flow when not working.
The needle valve stops fuel flow when the floats exert sufficient pressure to close the valve, otherwise there is no flow restriction as the needles are hanging down.

For the pump to continue ticking after filling the carb wells, and with a likely higher fuel pump pressure I suspect the carbs are leaking fuel inside the venturis, you will not see it unless you leave the ignition on and have the air filter removed. You may have poor closing carb valve (or valves), an easy fix.

Dave the cog.

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theelanman
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Re: SU fuel pump

Post by theelanman »

I was pointed in the direction of this.......

https://simonbbc.com/fuel-flow-su-repla ... fuel-part/

its now in my possession and will be fitted while they're painting the car.....

:D

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Lotus-e-Clan
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Re: SU fuel pump

Post by Lotus-e-Clan »

theelanman wrote:I was pointed in the direction of this.......

https://simonbbc.com/fuel-flow-su-repla ... fuel-part/

its now in my possession and will be fitted while they're painting the car.....

:D

Sounds ideal. I like the self-regulating bit ..and the PRICE :shock: !
Peter K

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rbgosling
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Re: SU fuel pump

Post by rbgosling »

theelanman wrote:I was pointed in the direction of this.......

https://simonbbc.com/fuel-flow-su-repla ... fuel-part/

its now in my possession and will be fitted while they're painting the car.....

:D
Not as cheap as my Facet-style one, but more handy having the correct mountings and fittings already present, and probably quieter too (I'd hope!).

If the Facet pump does stop working, this looks like the right way to go.
"Farmer" Richard

1990 Lotus Excel SE (Lilith)
2004 Jaguar X-Type Estate

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Re: SU fuel pump

Post by majcd213 »

Dave the cog, Do you have a link for the fibreglass repair on YouTube pls!?
When you have eliminated the impossible whatever remains, no matter how impropable, must be hit with a hammer

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