Fuel Pump question - Zetec on Carbs

[MJW16]

Hi all,

I have a confusing fuel pump situation on my 91' Super Sprint with a Raceline Zetec running on Weber 40's

When the ignition is switched on (engine not started) i would usually expect the fuel pump to tick for a few seconds max to prime and pressurise the fuel lines.  I've only had the car a week and quite often this is exactly how it behaves.  On a few occasions though, this afternoon included, the fuel pump just keeps ticking.endlessly and doesn't seem to achieve the pressure required to stop it trying to prime.

The car does start and run ok, and there's no sign of any fuel leaks.

It has an electronic ignition module, but running on carbs it has no ECU.  Therefore I'm assuming the system is as simple as a pressure switch of some sort on the fuel pump that makes it shut down when line pressure is reached and then run as needed to maintain that pressure once the car starts?

As a separate (but possibly related) issue, I have a mystery of a disappearing tank of fuel.

When I picked it up last week from Sevens and Classics it was handed over with a full tank of fuel.  I questioned this because the gauge only showed 1/4 full, but was assured it had been filled up that morning.  I have no reason at all to doubt this - the guys up there have been great and really helpful - so the conclusion was that there must be an issue with the gauge or sender unit that I'll need to investigate.

I drove it home to the Maidstone area, which is 18 miles. During that journey I reset the trip counter with the thought process that I'll drive it for 100miles or so then top it up to see how much I fit in the tank, and put a fuel can in the boot shortly as a back up until the gauge is fixed.

I took the car out for a little drive during the week, then today drove it back up to Sevens and Classics as they kindly helped with a couple of extra poppers and fixings needed.  As I drove away from them to head home, it ran out of fuel half a mile down the road.  The trip counter showed 25 miles, so with some of the original journey home not recorded, the most I've covered is 35-40 miles.

The guys came down the road with a Jerry can and rescued me, but nobody has any idea how the car could have run out of fuel 35-40 miles after being filled up.

I'm going to remove the filler pipe tomorrow to physically check the fuel level in the tank, and/or fill it up to the brim myself to confirm if there is indeed a fault with the gauge or sender.  I'll also get a petrol can in the boot to avoid getting stranded again!  But the disappearing tank of fuel is most confusing.

I will investigate and try to pin down the issue here,but thought it might be worth a forum post in case I'm missing something really obvious and silly.  If anyone has any ideas, or can see a potential link between the two elements detailed above, your thoughts would be very welcome.

Just to reiterate, there is no sign I can see of a fuel leak under the car.

Thanks

[OldAndrewE]

Can't help with the fuel loss but can only think the tank could not have been full.

What pump have you got?  I had a similar issue on a mini with a solid state Facet pump - it was an airlock in the fuel pipe.  The car would run but sometimes the pump would go mad.  Cured it by taking the pipe off the carbs and pumping loads of fuel through to remove the air.  It has been fine since

[Wrightpayne]

Couple of thoughts....

Filling sevens with fuel can be problematic and the filling nozzle can click off (frequently) even when starting to fill an empty tank. I generally know how much should go in based on mileage and the not so accurate gauge.

 

Re priming, as I understand it, carb cars should have a low pressure pump which shuts off when the carbs are full and the floats within the carbs shut off the fill valves. Possibly, one/both of these is not closing off? This would be accompanied with overflow of fuel either externally or into the engine (causing starting issues).

Ian

[Guy Lowe]

When my (Raceline) Zetec was on carbs I used a low pressure Facet fast road pump with a pressure regulator set at 3.5 psi. I didn't have a pressure switch just let the pump run continuously, worked faultlessly for years. 
 

I now run TB's with the same pump feeding a HP pump & swirl pot, again no pressure switch I just let both pumps run continuously without any problems. Both set ups are that recommended by Raceline.

[Benton]

Random thoughts......

If it ran out of fuel from a full tank after such a short time you would either have been smelling raw fuel escaping or excessively rich running (you could pull a spark plug and check condition), both I would have thought to be very obvious given the limited mileage you were able to cover.

Did it actually run out of fuel, how could you tell, or did perhaps the fuel pump just temporarily pack up / fuel pump couldn't drain any more of the tank (positioning problem, unlikely but...)  then by coincidence after putting a Jerry cans worth either it worked again or fuel level was OK then for the pump to work?

 

 

 

[garybee]

I'd be checking that the floats/needles were successfully shutting off the feed from the pump.  

[7 wonders of the world]

the tank wasn't full, someone has filled it till the nozzle clicked and assumed it was full......

a leak would be obvious as would a car doing only 5mpg...! - it would make a crossflow look like a Prius   

 

 

[ScottR400D]

As above, most likely explanation is that it just wasn't filled. First thing to do is simply fill it properly and then see what happens. 

I just see no way you could 'lose' a tank of fuel without being aware. 

[Colin Cooper]

I'm a bit surprised Sevens & Classics didn't sort the gauge out before selling the car to you.

I run a Raceline 2ltr Blacktop Zetec on 45's. Like Guy I don't think the pump has a pressure switch - it just runs. 

Col  

[ScottR400D]

Until it's been definitively filled and run again we don't know if the gauge needs any sorting. 
 

[MJW16]

Thanks Guys,

It is indeed a Facet Fuel pump in the boot with a Fuel pressure regulator in the engine bay (not sure what psi it regulates it to, it's a 'Petrol King Fuel-Saver' with a grub screw on the top I assume for adjustment, but no pressure values indicated).  There's no separate pressure switch as such and it's correct that the pump just runs all the time.  I would still expect it to stop clicking though with the engine not running and the fuel line fully pressurised.  There's no excessive fuel smells and it's running well so presumably not excessively rich.  It sounds like I'd better check a spark plug to confirm though, and somehow check that the fill valves in the carbs are shutting off when they should?

Regarding the disappearing tank of fuel, it would seem the mystery is solved.  I've filled it up myself this morning and fitted 34.5 litres in it.  Which means it was running pretty much on fumes again if the tank capacity is 36 litres.  The fuel gauge works fine too and is registering full.  So it appears there was a mix up when I collected the car and it really did only have >1/4 of a tank of fuel in it as per the gauge reading at the time.

Cheers

Mike

 

[Benton]

 Good to have a simple rational explanation sometimes 

[Wrightpayne]

I'd just run it and see!