[Spridgets] Fuel pump

Tue Jan 12 15:57:00 MST 2021

 After a cursory inspection today I found a non SU type electric pump.  Looks like a large Facet type, but I can't be sure.  I also found that there are no filters anywhere between the tank to the Weber.  I removed the cylindrical mesh filter in the Weber and it was absolutely clean.  So I started it up cold and for the first time right after start it idled a little over 500 rpm.  Usually with the jets (probably wrong ones) in the Weber startups have not been under 1000 rpm at idle in the past.  The pump was clicking away as normal.  It has rubber type fuel hose on either side of the pump which should not present a problem.  Don't want to, but might have to drop the fuel tank and have a look see.
Mike MacLean

    On Monday, January 11, 2021, 4:08:30 AM PST, GUY DAY <grday at btinternet.com> wrote:  

 #yiv6303893106 p{margin:0;}Hi Mike,
Please let us know what the problem / solution is after your examination. I don't know about any-one else but I would really like to know.

I wouldn't jump towards the blocked pickup if only because at a low speed fuel suction should be less than it is on the drive home. I take it you have a standard SU pump mounted in the normal under 'rear seat' position. If you have that would lean me further towards the fuel vaporization in the pump or pipework leading to it. 

Best of luck in searching,

Guy R Day

------ Original Message ------
From: "Michael MacLean" <rrengineer.mike at att.net>
To: grday at btinternet.com
Sent: Monday, 11 Jan, 21 At 10:57
Subject: Re: Fuel pump

I think you have the most thoughtful explanation so far. I will be under the car in the next few days and check for a leak in the fuel line or it's proximity to the exhaust. After it finally started the car ran normally all the way home. I doubt it was the diaphragm. Clogged pickup or vaporized fuel is more likely. Thanks for that.Mike M

Sent from AT&T Yahoo Mail on Android 

  On Mon, Jan 11, 2021 at 2:37 AM, GUY DAY<grday at btinternet.com> wrote:   Mike,

Let us consider this as the problem you experience rather than something at which we can throw random ideas (what is the first thing I do - throw in a random idea!) or past histories of different problems. If you are sat with the engine idling or with minimal use when inching forwards, the pump ticking should slow considerably.

Your wonderful description of the pump 'running furiously' suggests racing rather than running fast and that means no liquid fuel is in there. The pump will only race when it has no fuel inside it as the viscosity of the liquid stops it. If it is filling empty carbs or trying to compress a vaporized fuel line forward of the pump it will speed up but not race as there is fuel stopping the diaphragms from moving too quickly/racing. If it slowly builds up to racing it may suggest the fuel level in the pump is lowering as liquid fuel is pumped out and/or that that liquid fuel has stopped getting to the pump.

Possible reason: 

It can race if the fuel in the pump or the line between tank and pump has vaporized - the viscosity of the liquid fuel has gone leaving a gas behind. Is the exhaust pipe underneath it? You had a warm up run before you reached the slow moving line, exhaust heat is high. There is no air flow under the car to cool it down, radiated and convected heat is heating up things near to the exhaust - but I am presuming your exhaust runs in the proximity of the pump. But I'll bet the slow moving line you were in sheltered you from any ground level side drafts to allow cooler air to reach under the car and the pump. 

Other possible reasons:

Tank side fuel line with a pinhole allowing occasional air to get in. I would have thought rather unlikely. A damp patch around the fuel line may be evident.

Filler cap vent blocked. Reasonably common. 

Filter in tank gets blocked. Has the tank has been relined with with a 'slosh liquid' and filter not kept clear? A build up of original crud may be not enough.

Some pumps have a mesh filter on the pump side of the inlet union. 

Flexible pipe kinked or blocked. Unlikely as liquid fuel loss is at low speed.

Split pump diaphragm. Why should it mend as the motor runs at normal speed again? 

What the solution is without have a good 'look at' session I don't know. That it came in when fuel demand is at its lowest, ie the car isn't moving, could well be the key clue. Looking at something between the fuel in the tank and the pump is indicated, be it exhaust pipe heat or whatever..... 

Hope it helps.

Guy R Day

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