Ace Bristol Electric Fuel Pump

[Ron Hollis]

My car ran perfectly for decades on a nondescript SU pump mounted under the bonnet, instead of the original mechanical unit. It recently gave up the ghost. With no part number I replaced it with one suggested by Burlen Services. This is inadequate. Does anyone else have this configuration and could advise a pump specification?

[AC Ace Bristol]

.
Ron

I run electric SU fuel pump located in the boot of BEX333 and the original  mechanical pump.
I bought my SU Pump from Burlen in June 2016...........  Part number AZX1332EP    Electronic pump   (Positive Earth).
Short suck long push/ delivery.

Sorry I can't help you with the equivalent data for SU pump located under the bonnet when it will be long suck short push/ delivery.   
Caution Check positive or Negative earth.

All pumps are polarity concious i.e. either + or - earth.  Positive ground pumps have RED sealing tape, whers as Negative have Black sealing tape.
The pump will  be damaged if connected to incorrect earthing.

Keith

[TTM]

What model of pump did Burlen provide you with?

I run the exact same set up as Keith. I only use the SU pump to prime the circuit before starting the engine.

[Ron Hollis]

Keith, Thanks for the information and tips. Some motorsport cronies suggested Facet pumps but they only seem to be available with negative earth.

Hi TTM thanks for your reply. Burlen's suggested AUA25LP which they say was standard on the Aston DB2/4, mounted under bonnet. if you run with the electric pump off then it must become a restriction in the line, which the mechanical pump presumably overcomes.

[TTM]

Ron,

On my car the mechanical AC pump on the block and the electrical SU pump in the boot each feed one side of the fuel rail. If the SU pump is turned off thus not building any pressure into the fuel rail then the AC pump should have less pressure to work against, at least in most of the area in the [load; rpm] 2D map where both pumps do not need to run together to avoid the float chambers to run dry.
I have heard of folks running an SU pump in the boot feeding straight into the AC pump but as much as it may help with building "enough" pressure "when" needed I am not sure if this does not mess up with how the AC pump runs, as it is not designed to pump up fuel from a pressurised line, even if it seems to work. In fact using such a set up might even hide the symptoms of a failing AC pump, which is not desirable from a purely functional point of view.

When you say the new LP AUA25 pump you tried was "inadequate", what were the symptoms?

[Ron Hollis]

hi TTM, thanks for the explanation and your interest.
symptoms are- under acceleration, say on a long uphill (only because this is more convenient than running at high speed) after say 20 secs the engine cuts to four cylinders, we then potter for a short period whilst the affected float chamber refills and return to six. I have checked tank intake, renewed and enlarged the fuel line, replaced/cleaned all filters in line and carbs and checked needle valves/floats in carbs. A flow check to an open end at the carbs gave a flow of 7.5 gallons/Hr; this would reduce if flow was through  the needle valves.   

[TTM]

Hi Ron,

Which float chamber runs empty and at which height do you have the floats set at?
If the float chamber of the front carb runs empty under the conditions you described then I would be tempted to think that your previous pump was a high pressure unit if the issue appeared only just after replacing it with the new low pressure unit.
You may want to simply repair your previous pump with spares that Burlen may be able to provide you with, assuming it can be repaired. That won't tell us if the old pump is a high or low pressure unit but at least this would fix the issue.

[Ron Hollis]

Hi TTM,
Don't know and tricky to establish, I would have to turn engine/pump off as it cut to 4 cylinders and expose the three float chambers, roads too busy round here. My engine has Weber carbs and float levels are as makers settings.
I ditched the old pump when Burlen's seemed confident. Now they are understandably reluctant to be specific on a pump for an engine that didn't have one originally; that's why I tried the forum.
Their high pressure AUA25 has a lower duty (7gph), so not encouraging.
Burlen's data is also confusing, giving the duty of AZX1332 as 15gph in their duty schedule (technical section) and 7gph on the sales page. In a mail they confirmed it as 7gph. It would be interesting to know if Keith's engine runs on the electric pump or if he just uses it as a primer like you.

Thanks for your interest.             

[TTM]

Ron,

For what it's worth I used to run the engine on both pumps until I noticed it would run just as well whether the SU pump was on or off, but that is on a car run on the road only so Keith or others who also track their cars may provide more complete feedback.

Where do you have the SU pump mounted?
It seems to me that a LP pump should be always mounted anywhere in the engine bay above or close enough to the level of the float chambers. I am not sure how this can be done properly on an A.C. Bristol where the carbs, Solex 32 PBI or Weber (34 ICH?), have their float chambers at about the highest point of the engine bay.

Float chambers are surge tanks which ideally should remain full under all running condition. If they run empty then I would imagine it is not just the flow of the pump that is insufficient but also the delivery pressure, especially when relying on only one electric pump like you do. I could be all wrong but since you clearly stated that your engine started to run wrongly after only replacing the fuel pump then I keep thinking this is the root of the problem in your particular, non-standard set up.

[Ron Hollis]

Apologies for the delayed conclusion. The solution was to refit the original mechanical pump and retain the LP electric pump mounted in the engine bay on the passengers footwell bulkhead. The LP pump primes the osystem ok and the two together satisfy the engine in road use without flooding. Thanks for your advice.

[TTM]

Ron,

Good to see you were able to solve the problem and thank you for posting back about it. Enjoy!

[ian wayne]

It seems the topic of running both electric and mechanical pumps has been flogged about quite a bit, but there is one part I am not clear on.  if the desire is to use, say, a boot mounted SU pump ONLY to prime the fuel line up to the mechanical pump, is it acceptable to just insert one into the existing line?  This would be a lot less work than running a secondary line to the carburettor fuel rail. I can think of an alternative to that by using a  couple Y pipes and a one way check valve around the electric pump, but that may not be necessary.  My basic concern is, what king of impediment does a non-running electrical pump present when presented with suction (from the mechanical pump) on its output side?  If it is negligible, then just running it in-line should work.  Advice, anyone?

[TTM]

I have heard of someone adding an electrical pump to feed straight into the back of the AC pump without having any issues, although I did not hear of all the details involved, especially regarding suction.

Edited to add : oops, I just realize I mentioned this earlier in this topic already.

[AC Ace Bristol]

Ron

Both fuel pumps ( Electric SU & the AC Mechanical ) have separate feed from tank, one from either side of the fuel tank,  My electric SU pump in the boot is used to prime the Solex by cutting into fuel rail and feeding front Solex first whilst the mechanical pump  feeds  the rear  Solex first.
On continental runs when touring with mainly Cobras  I  often run both pumps to ensure adequate fuel supply. ( otherwise I have problems keeping up with
the V8s)
The  rubber ?  diaphragm  in the AC mechanical fuel pump can be effected by modern fuels  and should be checked and replaced regularly.
On the ACOC  Luxembourg  International,  I rebuilt the The AC mechanical pump , but I found it could not supply enough fuel due to fuel vaporisation ,
mind you we were driving in  temperatures of 39 /41 degrees C.  ;)
 
One or two of the racing Ace Bristol's  have a small  fuel reservoir in line under the bonnet so they always have  a continuous  fuel supply especially when
low on fuel and cornering hard.  ;)

Hopefully  the above is of interest and you resolve your problem.

Keith

[ian wayne]

Thank you Keith, this is very helpful.  It seems that if I want to do it right, that second fuel line is the way to go.