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vapour lock problem solved 444-544

posted by  gert 444 on  Thu Sep 9 08:14 CST 2004
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last visit: Wed Oct 22 04:11 CST 2014
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Some time ago I asked you how to solve the vapour lock problem, that my PV444/B20F demonstrated with each and every hot start. I got a lot of good advice, but had to find out the solution myself....
Isolating the fuel hose didn’t help and the fitting of a large stainless steel heatshield between the HIF SU”s and the manifold didn’t help anything either, to my surprise. Then I knew it just had to be the fuel pump and mounted an SU electric fuel pump. Problem solved.
The question that remains of course is would a heat shield in front of the fuel pump have been a solution as well. I might try that one day.

What I also did was replacing the rear HIF SU with a slightly different one, that had the vacuum take off for the distributor on top instead of under the carb housing. I never saw it mounted at the underside before and there also had to be something wrong with that particular carb, because often –during hot starting- fuel was leaking out through that “upside down” vacuum take off (and not where you would expect it to leak: through the overflow pipe).
Also I’ve got a choke mechanism now on both carbs instead of one, though I didn’t connect the choke on the rear carb yet. It just doesn’t seem to be necessary as cold starting isn’t a problem at all. And hot starting isn’t a problem anymore either now –to my great relief.







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    vapour lock problem solved 444-544

    posted by  Bennie on  Thu Sep 9 08:42 CST 2004
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    last visit: Wed Nov 28 03:03 CST 2007
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    Good to hear you solved the problem Gert, little things like this can be a real PIA to track down sometimes.

    Only I was just wondering: you say you replaced the fuel pump for an electric one, and swapped a leaking SU with an other. Are you sure the problem was actually in the pump, not the carb? (in other words, a too-lean-to-start (vapour lock) or a too-rich-to-start (carb overflow) problem)
    Also, did you try an other (mechanical) pump? I wonder if the problem was structural (over)heating of the pump, or just a faulty pump.

    Cheers, Ben
    --
    P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)








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      vapour lock problem solved 444-544

      posted by  gert 444 on  Thu Sep 9 09:23 CST 2004
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      last visit: Wed Oct 22 04:11 CST 2014
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      All I can say at this moment is that the electric pump solved the problem. The -occasionally- leaking carb was replaced a few days later. But I agree it would be interesting to know if the replacement of the carb would have solved the problem as well. It would make some sense, because why would I be the only one with a B20 needing an electric fuel pump...?
      I will reconnect the mechanical pump to find this out and I'll let you know the results.







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        vapour lock problem solved 444-544

        uid 10468's pic
        posted by  yogui on  Fri Sep 10 03:18 CST 2004
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        last visit: Tue Apr 30 15:41 CST 2013
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        You could be test the mechanical pump with kerosene (more safe than gasoline), as indicated on Haynes manual.







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          vapour lock problem solved 444-544

          posted by  someone claiming to be mjamgb on  Fri Sep 10 05:34 CST 2004 [RELATED]

          Pumping agains a head may be an issue for the old pump, i.e. cracking the needle valve open that first time, due to a leaky check valve. That, coupled with a plugged vent in the HIF could have caused some real issues.

          Will be interested to know what sort of pressure your pump can produse and hold. That could be tested w/o mounting to the car as it would only take a couple manual strokes of the pump lever, a piece of tubing and a pressure gauge.

          Mike!








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            vapour lock problem solved 444-544

            posted by  gert 444 on  Fri Sep 10 08:30 CST 2004
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            last visit: Wed Oct 22 04:11 CST 2014
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            Well, I suppose it won't come as a surprise to the experienced that the problem appeared to be the carb and not the pump, as Ben already suggested.
            I reconnected the original mechanical fuel pump today and guess what: no starting problems whatsoever! So I've put the SU pump back where it came from: the trunk of my '54 Morris Minor (where it sat for years as a spare one).
            Obviously an electrical pump can handle a faulty carb better than a mechanical pump. Because of larger pressure perhaps?







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