16 replies to this topic

[PaulColeman]

Okay, we had an epic fail on yesterday's London to Brighton which you can read about here... http://www.theminifo...-l2b-epic-fail/

 

I've got problems with the fuel system and I'm more than confused! The car in question is a 1976 Mini 1000 with everything standard, no mods at all apart from the points being replaced with an electronic version.

 

The car broke down yesterday a few times... the first was muck in the float chamber valve which starved it of fuel. I managed to fix that by the side of the road but then a while later there was fuel pouring out of the top of the float chamber - from under the pipe which feeds the fuel in. So my first question is - is there a vent hole that's supposed to be there? It only seems to happen when the car is warm so I was thinking it was a crack or pinhole which expands as it warms up? However, there shouldn't be fuel at the top of the float chamber anyway so the valve must be stuck but it didn't seem to be.

 

Now for the next (possibly very related problem)... when I stopped the car yesterday and took the pipe off the top of the float chamber there was fuel spurting out the end of the pipe. But the fuel pump is a stock mechanical one so how the hell is it pumping fuel with the engine off? I wondered if it was a syphoning thing and took the fuel cap off but it carried on pumping away? Even after 5 or 10 minutes it was still pumping like a good 'un. I don't understand!!!!

 

Are the two things possibly related? Anybody got any ideas as to what I can try next?

 

Thanks, Paul.

[Stevie W]

Hi Paul,

So sorry to hear about your L2B disaster! Sounds like you & your daughter had a bit of a day!

I've recently had exactly the same issue as you, with fuel piddling out of the overflow on my right hand carb.
There's a hidden overflow pipe behind a plate just below the fuel inlet and it was pouring out of there straight onto my hot exhaust manifold.....scary!

The Burlen fuel Co in Salisbury sell a kit to prevent this, which I've just bought two of.
The kit comprises of a new ethanol resistant float (ethanol is present in modern unleaded fuel), a new float chamber gasket and a viton tipped float needle. This is supposed to eliminate fuel overflows. I also set the gap between the float arm and float chamber lid edge to that specified in the Haynes manual. This makes sure the fuel level in the float bowl is not excessively high.

At £20 a go plus postage, there a bit steep but better than having fuel piddling out!!!
I fitted mine last weekend and so far so good.....I'm not sure what's going on with your fuel pump though.

Cheers, Steve

[dklawson]

If the engine is hot, the pump mechanical, and if the fuel line runs near the exhaust pipe/manifold there is the possibility that the pumping fuel you observed is caused by percolation from heat.  This is purely a guess on my part.

 

Does your car have an HS or HIF carb?  (Sorry, I don't know what would be on a '76 as standard and yours may have been changed anyway).  An HS series carb will have the separate fuel bowl to the side with 3 screws holding the cover on.  Some covers have a vent hole, others have a vent nipple to which you can connect a hose to divert overflowing fuel away from the hot areas.  Hopefully you have this type of carb because they are easier to deal with regarding the float valve.  Assuming it is an HS series, remove the bowl lid, remove the float and float valve from the lid.  Inspect the float valve and replace it if the tip has any wear or witness marks.  Inspect the float and replace it if there is any fuel inside.  Se the float valve per your service manual.  Clean any and all sediment out of the float bowl before refitting the lid.  If you do not have a fuel filter before the carb, install one now along with some fresh rubber hoses.  With the float valve replaced and set, a float without leaks, and a new filter before the carb you should be protected from both fuel starvation and stuck open float valves.

[PaulColeman]

Thanks for the replies and thoughts/suggestions guys. My daughter's car has the stock HS carb with the float chamber next to it with 3 screws as you described. I thought yesterday that the top had a crack in it but now I realise it's a vent hole. There is nowhere to connect a hose onto though it must just have a small hole (eyesight's not that good so I haven't actually seen it!!).

 

Is it possible that there is too much pressure from the pump and that it's pushing against the valve and actually forcing fuel in there even though the valve wants to be closed? With my thumb over the disconnected fuel pipe it was squirting quite a way when I let go. I thought fuel pumps were only a few psi (like 3 or 4).

 

I will remove the valve tomorrow and see if I can see any marks on it - I'm still too knackered from yesterday to work on it now!!

 

Cheers, Paul.

[Stevie W]

Hi Paul,

Yes the fuel pump should deliver 3-4psi which a healthy needle valve should be able to cope with!

The standard needle valve is just a brass against brass seal, which is ok when new and not worn.

Cheers, Steve.

[PaulColeman]

I might just replace the valve (to eliminate it) but this only happens when the engine is hot?

 

Paul.

[dklawson]

The fuel pressure should be about 2.5 PSI, not up to 4 PSI.  While some carbs in good condition with new float valves can handle the higher pressure, the spec is actually closer to 2.5 PSI.  If your float valve is not fully closing then any pump can/will overpower the valve and you will be able to pump fuel out of the carb through the bowl lid vent AND into the main metering jet in the carb causing flooding.

 

Remove the float bowl lid, then remove the float and finally the float valve components.  Inspect the tip of the float valve needle and replace the valve if there are any witness marks on the tip.  The Viton tipped mentioned by Stevie W are what I use these days.  They work well for my cars.

 

It's amazing what you can find quickly on the web.  The picture below illustrates worn and new float needle valves.

 

[PaulColeman]

Okay, I'll pull it tonight and have a look - I was too knackered last night after my London to Brighton fiasco!!

 

Thanks, Paul.

[PaulColeman]

Well I pulled the valve and it does have a mark all the way around. I tried to take a photo but it's difficult to see...

 

I'm hoping this is going to be the source of the problem and I'll buy another one.

 

Cheers, Paul.

[Stevie W]

Hi Paul,

Yes that looks a little worn, a new one should sort the problem out!

Cheers, Steve

[PaulColeman]

I really hope so! I've bought just the valve (viton tipped) as the float looks fine.

 

Why would it only leak when the engine is hot though? I don't understand!

 

Cheers, Paul.

[Stevie W]

Hmmm

That's a strange one! I'd fit the new needle valve and see how you get on!

Report back here if you still have overflowing problems after fitting the new needle valve and we'll have another think about it.

Cheers, Steve.

[KernowCooper]

When you fit the new needle valve and seat I'd check the float level to see if your is high and needs a washer under the valve

Edited by KernowCooper, 20 May 2014 - 07:54 PM.

[PaulColeman]

When you fit the new needle valve and seat I'd check the float level to see if your is high and needs a washer under the valve

Okay, is that a common problem? It didn't look as though the float height is something you can adjust normally?

 

Cheers, Paul.

[KernowCooper]

Yes its something you check if you have the top off, see below the two types of floats early and late plastic

Attached Files

•  float level early.png   21.84K   3 downloads
•  float level plastic float.png   38.44K   9 downloads