23 replies to this topic

[Boycie]

Hi all.  My 1981 Mini City is usually very reliable, but has recently been causing me grief.

 

Standard 998cc car, single HS4 carb.

 

 

The car starts straight away from cold, and runs fine.  My routine is always to let it fast-idle for a few minutes before driving off, progressively letting the choke in until the idle is approx 1200 rpm.  (as I've been doing for 25 years).

 

At this point, after a minute or so, the car will splutter and cut out.  Sometimes it will restart with lots of churning, sometimes I give up and take the modern car to work.

 

When I inspect it, the carb float chamber is always dry, the pump apparently isn't pumping.

When I remove the fuel feed pipe to the float chamber, and turn the engine over, fuel splurges out at an enthusiastic rate...

 

I then reassemble everything and the car will then start and run perfectly normally for the rest of the day, with no hesitation, even at high revs or up long hills.

 

Anyone had this before?  It doesn't make much sense to me!

 

[cal844]

Make sure your fuel hose connectors are tight. Sounds like either air getting in somewhere or a failing pump

[nicklouse]

The diaphragm can fail. Normally related to petrol in the oil.

[Boycie]

Thanks both.  I have no fuel in the oil, well, none I can reasonably detect anyway.  Fuel hose seems all ok.  No running issues apart from this!

[nicklouse]

Then I would be looking at blockages in the fuel line to the pump.

[GraemeC]

Sucking up crud in the bottom of the tank and blocking the pick-up pipe?

[Boycie]

I don't think there's any fuel feed problems.  When I was initially trying to diagnose the (first) breakdown, I took the rubber hose off the pump inlet and fuel poured out of the hard line that runs from the tank, just from gravity.

 

That's not to say there isn't something in the tank obscuring the pickup... but the problem only happens a few minutes after a cold start.  The unreliability is very reliable!

[Aly-g]

Have you checked the float and valve in the float chamber on the carb , could be sticking ? Maybe strip the float assembly and give a good clean.

Allan

[GraemeC]

I don't think there's any fuel feed problems.  When I was initially trying to diagnose the (first) breakdown, I took the rubber hose off the pump inlet and fuel poured out of the hard line that runs from the tank, just from gravity.

 

That's not to say there isn't something in the tank obscuring the pickup... but the problem only happens a few minutes after a cold start.  The unreliability is very reliable!

 

I'd still check it - if its crud in the bottom of the tank it won't get sucked to the pick up under a gravity flow, only when fuel is being drawn out with a pump.  And the few minutes is consistent too as it will take time to draw the crud to the pick up, in fact it may sit at tick over for hours quite happily, and only be a problem when the fuel demand increases with revs.

[Chris1275gt]

I had similar problem the filter in the tank was blocked and loose on the pipe in the tank. When the engine was not running the filter dropped 10 mm and hit the bottom of the tank which allowed the pump when starting to fill the float chamber after a very short while the suction caused the filter to be sucked up the pipe and cut the flow off. I’d changed the pump and renewed the float assembly which only left the fuel lines as the problem. so I’d throw a new fuel pump and float assembly on to check it’s not those components failing then your only left with the fuel lines and tank.
It will save you from going mad like it did me trying to second guess it!

[Homersimpson]

It might also be worth checking that the vent on the petrol tank is free and clear

[Boycie]

Thanks everyone, plenty to look at this weekend (if it stops raining!)

[Boycie]

I had a look at this again today.

 

Started from cold, sat there idling... no problems at all 

 

I peered into the fuel tank with a small torch.  Tank is clean, with no debris, rust or shale at all.  I can see the metal pickup pipe hovering an inch or so above the base of the tank, there's no filter or evidence of one in there.  I guess it's lost it some time in the past 40 years.

There's an inline filter in the hose coming from the tank, located on the rear subframe (I put it there when I last changed the fuel hoses) but that's clean with only minor debris.

 

So I think I'll change the pump, rubber hoses and filter.

 

What's the situation with new mechanical pumps at the moment?  The genuine pump from Burlen is out of stock.  Are Minispares ones any good?  Or go electric?

[Woolfie 640]

Had a similar problem and replaced it with new pump . Replacement mechanical pump was a copy of the original and the lever didn't appear to be the correct contour which meant not enough fuel getting pumped to carb when under load . Ticked over ok but bogged down after 2000 revs. Be careful where the pump is manufactured.

[1984mini25]

I had a look at this again today.

 

Started from cold, sat there idling... no problems at all 

 

I peered into the fuel tank with a small torch.  Tank is clean, with no debris, rust or shale at all.  I can see the metal pickup pipe hovering an inch or so above the base of the tank, there's no filter or evidence of one in there.  I guess it's lost it some time in the past 40 years.

There's an inline filter in the hose coming from the tank, located on the rear subframe (I put it there when I last changed the fuel hoses) but that's clean with only minor debris.

 

So I think I'll change the pump, rubber hoses and filter.

 

What's the situation with new mechanical pumps at the moment?  The genuine pump from Burlen is out of stock.  Are Minispares ones any good?  Or go electric?

 

Could you take a picture of your fuel filter arrangement on the rear subframe please. 

 

As I'm currently in the possess of derusting the inside of my tank as I'm having the same symptoms (and backfiring/clouds of back smoke if tried to be driven) and rusty sediment in the carb float bowl. 

 

I'm using a radiator flush, as I can't get hold of any evapo-rust locally or at short notice due to not having any stock (must be why its on sale) I'm going to have to clean the inside of the tank out as best I can, fit a filter to stop the fine stuff getting to the pump and carb and do a proper full clean and sealing over the summer.