10MPG!!! Is there a hole in my tank?!

[AndrewSkinner]

I realized the other day that i was spending allot of money on petrol for my 1959 Morris Minor 998cc.

When i actually sat down and calculated it i realized that my car is doing LESS THAN 10MPG!!

I cant afford this for much longer! What could it be??

I have replaced the float valve and seat, new points & condenser.

I have also checked that there is no fuel dripping from the carb onto the engine bay and i have also bent the float chamber further up so that the float valve closes sooner (Only fills up 3/4 of the way) because i was worried that it was floating to the top and then sticking up.

I can hear the petrol pump go a bit mad when decelerating and the engine slows down near to idle speed. The ticks then slowly slow down as the car stops??

Sometimes the car will be idling and the petrol pump will go mad for a few seconds and then slow down again??

[Kevin]

Sometimes the car will be idling and the petrol pump will go mad for a few seconds and then slow down again??

Normally that only happens when sitting in hot conditions in a traffic jam, I had a similar thing a few years ago although the fuel consumption had got nowhere near that bad, and then one day I looked behind just after pulling away and noticed a wet trail behind convinced I had a water leak I went home but in checking it was all OK, then I noticed the bulkhead below the fuel pump had a stain mark running down it, on removing the pump I found that there was a fracture between the 2 lower halves between 2 of the retaining screws, I no this is not a usual fault but 10mpg from yours must be fuel related is the fuel line good and secure especially the pump to carb one, is the tank sound as they can become porus with age.

[AndrewSkinner]

Thanks for your reply! i think that the fuel tank is ok? i will check it tomorrow in the daylight and also the piping. i did not think of that? the fuel pump may be cracked!

I am sure that it is not running rich as i have set the carb recently and i dont think that it would even run if it was that rich!

[Willie]

If the tickover and general running are normal then I would expect you to be able to smell the leak, especially in the boot if it is at the tank end.
It is fairly common to have a pump which is erratic on occasions but it doesn't matter,if there is no leak,because the petrol can only fill up the float bowl and then stop.

[svantemann]

[quote="AndrewSkinner"] I have also bent the float chamber further up so that the float valve closes sooner (Only fills up 3/4 of the way) because i was worried that it was floating to the top and then sticking up.

The needlevalve opens when fuel level goes down, and close when float rises as more fuel comes in the chamber. If you bend float further up, it means your needlavalve close later. If you want the needlevalve to close sooner you will have to bend the float down - to lower the fuel level in the chamber.

About your car using to much fuel, chek the ignition timing and the points gap. One of my cars had the same problem, and after setting the ignition it use just half the fuel ( it was a lot out of timing, but car could start and drive ok ) This MIGHT be your problem.

Regards
Svantemann

[bmcecosse]

I assume the bending 'up' was done with the float lid upside down - and so in effect was being bent 'down' ! I hope so. Simple test - switch on ignition and listen to the pump - dose it 'tick' steadily ? Should hold firm after initial slight ticking then stop. Provided it's not flooding over, then the most likely reason for poor MPG is choke not going off properly. But also have a look at the air filter element - is it choked solid with muck and oil fume ?

[Pascal]

I've got a similar problem; though not quite as bad. I've done about 160 miles with 32 litres, so that's about 23 mpg, about a third on motorway (55mph) and the rest in town, mostly on short journeys. Could that explain the 23 mpg or is that still not enough?

I've checked the fuel system and couldn't find any leak, however I've noticed a wet trail behind the exhaust pipe. Does that mean the fuel mixture is too rich?

I've looked in the Haynes manual how to adjust the mix and they say to lift the piston by 8mm with a wire spoke or small screwdriver, however I don't understand where you insert it. Can anybody clarify?

[jackkelleher]

If you remove the air filter, there is a clear view (and prodding space) down the air duct to the piston. It's the curving metal wall that you can see blocking your view.
Be careful not to lift the piston too high, the revs go down misleadingly- I did that the first time!
Hope this helps,
Jack
ps if the trail is water, it's apparently just from short runs. But that's not really my area of expertise (if I have one). 23 mpg sounds a bit low- it's generally meant to be about 30, I thought. You can calculate what it should be for the distance and road types you've done with the figures in the front of the Haynes... That glorious bible

[bmcecosse]

Known as HBOL - Haynes Book of Lies!

[Kevin]

they say to lift the piston by 8mm with a wire spoke or small screwdriver, however I don't understand where you insert it. Can anybody clarify?

I just looked in my Haynes are you are correct it does say that (never noticed before) but its incorrect
there is a small piston lifting pin underneath and you use you finger to lift it but only by 8mm or 1/32" to check the mixture I have not heard of using a wire or screwdriver to do this and dont know how you could anyway.

[alex_holden]

I noticed that too. I think Haynes got it wrong because in the official workshop manual it says "1/32 in. (.8mm.)" - Haynes lost the decimal point when they copied it so it says "1/32 in. (8mm.)." which is nonsense - 8mm is 5/16".

The wire method is what you're supposed to do if the lift pin is stuck or you've got a carb that doesn't have one. You can lift the piston with a stiff wire while the engine is running - I tried it. The idea is that a wire doesn't obstruct the airflow the way your finger would.

[AndrewSkinner]

Hey guys thanks for all your help!

you will be glad to know that the car is fixed and now returning a mpg of around 40mpg!!!!!!! YAHOOO

Just in case your interseted it was the pipe from the petrol pump into the float chamber. although it had a clip on it and it felt tight it was infact dripping out of there while driving along

A new tight clip and new hose got her back on the road in no time!! there are still a few petrol stains on the crossmember (Just below the petrol pump) but for now i am happy!!!

Thanks again for your help!! dont know what I would do without the trusty MMOC!

[jackkelleher]

Oh, well done! That's one of those problems that takes ages to spot, isn't it. I had that one, too, only slightly worse; the car had older wire-wrapped fuel line between the carb and pump, and I opened the bonnet one day to find petrol spurting out at hundreds of points through the mesh! Serious disintegration... A new fuel line fixed that. Well, good luck with your Moggy.