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Re: [Healeys] Fuel pumps (AGAIN!)

To: healeys@autox.team.net
Subject: Re: [Healeys] Fuel pumps (AGAIN!)
From: Bob Spidell <bspidell@comcast.net>
Date: Thu, 29 Nov 2018 10:14:12 -0800
Delivered-to: mharc@autox.team.net
Delivered-to: healeys@autox.team.net
References: <000001d48766$6e023780$4a06a680$@cosmos.net.au>
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Now THAT'S a new data point.  I was confused as to why SU pumps came in 
'low pressure' and 'high pressure' but it appears 'high pressure' is 
relative:

http://sucarb.co.uk/technical-electrical-fuel-pumps

So, the HP pumps are meant to be mounted near the tank.  Usually, these 
are quoted to be 3psi, so your estimate is pretty close. Still doesn't 
explain why some of us 'claim' to have had issues with them.

Bob

On 11/28/2018 2:05 PM, Larry Varley wrote:
>
> Hi Group. Something worth considering when dealing with SU carburetors 
> and fuel pumps. I have been doing some investigation and testing the 
> effects of fuel pressure on SU carburetors. The image attached is the 
> correct specification for SU fuel pumps for the brass float version 
> carbs. The SU HP pump is quoted as 48 inch( petrol ) lift which is 
> about 1.5 PSI. This document is from a 1950â??s workshop manual. I have 
> tested one of my cars and the SU pump sold by all of the usual 
> suppliers has a petrol lift of over 10 feet. I estimate at least 2.5 
> PSI. I had my brother test his Healey 100 also and the same result. 
> The test was conducted attaching a clear plastic line from the fuel 
> supply line up in the air to show the lift. We have both fitted 
> pressure regulators and using the clear tube method set the pressure 
> to 48 inches ( 1.5 PSI ). The result in both cars that have wide band 
> oxygen sensors fitted is an immediate improvement in air fuel ratio at 
> idle, moving away from overly rich mixture. Both cars maintain a far 
> better and regular idle as they are no longer running rich at idle. I 
> believe that the carbs are barely able to maintain a constant fuel 
> level in the float bowls when the pressure is 2.5 PSI and that 
> pressure pushes the fuel level up in the bowls when the engine is not 
> consuming much fuel. At all other speeds both engines fine with good 
> air fuel ratio at 1.5 PSI fuel pressure.
>
> Regards
>
> Larry Varley
>
>

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    <p>Now THAT'S a new data point.  I was confused as to why SU pumps
      came in 'low pressure' and 'high pressure' but it appears 'high
      pressure' is relative:</p>
    <p><a class="moz-txt-link-freetext" 
href="http://sucarb.co.uk/technical-electrical-fuel-pumps";>http://sucarb.co.uk/technical-electrical-fuel-pumps</a></p>
    <p>So, the HP pumps are meant to be mounted near the tank.  Usually,
      these are quoted to be 3psi, so your estimate is pretty close. 
      Still doesn't explain why some of us 'claim' to have had issues
      with them.</p>
    <p>Bob<br>
    </p>
    <div class="moz-cite-prefix">On 11/28/2018 2:05 PM, Larry Varley
      wrote:<br>
    </div>
    <blockquote type="cite"
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        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D">Hi
            Group. Something worth considering when dealing with SU
            carburetors and fuel pumps. I have been doing some
            investigation and testing the effects of fuel pressure on SU
            carburetors. The image attached is the correct specification
            for SU fuel pumps for the brass float version carbs. The SU
            HP pump is quoted as 48 inch( petrol ) lift which is about
            1.5 PSI. This document is from a 1950â??s workshop manual. I
            have tested one of my cars and the SU pump sold by all of
            the usual suppliers has a petrol lift of over 10 feet. I
            estimate at least 2.5 PSI. I had my brother test his Healey
            100 also and the same result. The test was conducted
            attaching a clear plastic line from the fuel supply line up
            in the air to show the lift. We have both fitted pressure
            regulators and using the clear tube method set the pressure
            to 48 inches ( 1.5 PSI ). The result in both cars that have
            wide band oxygen sensors fitted is an immediate improvement
            in air fuel ratio at idle, moving away from overly rich
            mixture. Both cars maintain a far better and regular idle as
            they are no longer running rich at idle. I believe that the
            carbs are barely able to maintain a constant fuel level in
            the float bowls when the pressure is 2.5 PSI and that
            pressure pushes the fuel level up in the bowls when the
            engine is not consuming much fuel. At all other speeds both
            engines fine with good air fuel ratio at 1.5 PSI fuel
            pressure.<o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D">Regards<o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D">Larry
            Varley<o:p></o:p></span></p>
      </div>
      <br>
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