Help with MPG

[mickeytwonames]

I've just got a 1954 Mk II split screen (948) back on the road after finding it rotting like a badger in a field. The cars got it's MOT
I have redone the carb with a repair kit (new needle etc) and have reconditioned the distributor - the timing and all things related (tappets, mixture, plugs) are set correctly. The tyres are original cross plys set to the recommended pressure; however, and I'm fairly light on my right foot, I only seem to be getting 25mpg. Any ideas of how I can improve efficiency?

[faversham999]

I get 32 MPG from my 1961 948 2 door checked over 4000 miles using the Morris spedo wich I know is inaccurate

[Jefftav]

Welcome, You might get more answers if you post in the mechanical section.

You seem to have checked the obvious things but after a long run at fairly constant speeds what colour are the cars spark plugs, they should be a biscuit type colour if white or black something is upsetting the fuel/air mixture.

Also how are you working out the MPG as the morris mileometer isn't the most accurate of things and at this time of year you may spend more time running on the choke which will drastically lower the MPG. If you do a lot of start stop in town running then again MPG will be affected.

[simmitc]

Check that you don't have a binding brake. Is the odometer accurate? If a previous owner has changed the diff, then the speedo may be reading wrong. Find a known length of road to check.

[robedney]

Do what simmitc said -- check the brakes. If it's been sitting for any length of time you may very well have some rust in one or more of the brake cylinders, causing one or more of the brake shoes to stay in contact with the drum -- or be very slow to release. You can ask me how I know if you want to. Jack the car up -- each wheel should spin (neutral, hand-brake off for the rears) freely. If you've not done it yet, you should really inspect the brakes carefully.

[robedney]

And, it's really easy to check a speedometer/odometer for accuracy these days. If you got a smart phone (iPhone, Android, etc.) there are free apps available that use GPS for measuring speed and distance traveled. These are quite accurate. You can use one of these apps to compare to the speedo in the car and make corrections.

[bmcecosse]

Just compare with the flashing 'speed' signs to get an idea about the speedo - but even if it is correct - the mileometer could be well out. As above - check plug colours and report back. But short journeys/cold weather are killers.

[moggiethouable]

I dont think I am alone when I say that having spent years utilising strobes and fitting numerous new parts to various engines, sometimes it is better to get the car tuned at your local dyno garage first, possible faults are spotted very quickly or eliminated.
They can also check compression and the general health of the engine.
I accept that "the lord helps those that helps themselves" but now and again an independent eye coupled to technology can save a lot of Brass in the long run.
That way one can verily adopt the truism "if it aint broke dont fix it" and save money too.

[bmcecosse]

For a standard engine (even a lightly modified engine) a 'dyno' is a huge waste of money. There is so little to adjust on a standard engine - it really couldn't be easier....... Plug colours are the first check. Then we will get to the ignition.

[moggiethouable]

Yes if it cost mega bucks I would agree,around these workin' class parts 25-30 quid gets a complete read out and tune though.
The beauty of the mog engine is indeed its simplicity, the man has done much to alleviate his mpg issue,but the problem remains and can be helped rapidly with the minimum of outside sourcing is my point.
At this time of year and at my time of life and in these temperatures the attraction to get down and dirty oneself aint what it used to be of course.
Much can be learned on an occasional visit of this type also, even by the time served such as my self.

[mickeytwonames]

Many thanks for all your help - plugs out tomorrow morning!

[bmcecosse]

Aaaah - the plug check should be done during a long hard run. Get the engine nice and warm, at least a 5 mile run, then a good blast for a mile or so and switch off at speed and drift to a halt - no idling. Up with the bonnet and whip the plugs out. What colour do you see??

[chickenjohn]

Average driving you should be getting in the high 30's MPG and up to 45mpg on a run. These are the figures I got from my traveller. When in regular use I would get 38- 39mpg averaging driving to work, shopping, a motorway run once a week, A road driving. On a long run, 44- 45 MPG. There are few modern cars that can beat this economy in the real world.

Maybe your valves need grinding in? Or your points are set way out. or the air filter is blocked. Or the engine is generally knackered.

First of all though, set your tyre pressures, should be 26- 30psi for best compromise of ride and economy.

Should be getting much better than 25mph!!!

[MarkyB]

Tuning apart, I have a feeling that one of the benefits of radial tyres is less rolling resistance, hence better fuel consumption.
I'd expect the best part of 40 mpg normally, you don't carry a spare engine and gearbox in the boot do you?

[Trickydicky]

Got to agree with others on the tuning, I found that the problem with older cars, is that the diagnostic machines dont take into account the age of the engine.
True, they will tell you what needs adjusting and replacing but they wont take into account the age and wear in the engine.
Best indicator will be as BMC says the "colour of the plugs" after the engine is nice and hot.

Check the plugs after a good run, it will tell you if the ignition is set up correctlly. Then if they show the correct colour you can eliminate ignition problems.

Richard

[bmcecosse]

Plug colour is for mixture - the timing is set by the 'not quite' pinking routine....... But one thing worth testing is the vacuum unit - is it working as it should? It's there party as an economy device. If it's not working then the engine will be 'flat' and unresponsive. And poor on economy!

[mickeytwonames]

Many thanks all your 'sparky' replies.
To paraphrase The Mamas and the Papas, California Dreamin'

All the plugs are brown and the smoke is grey
I've been for a drive on a winters day
I'd be safe and warm without 4 X ply
Morris Minor weaving on such a winters day

Solution adopted from advice given

• Front off-side wheel binding slightly - now free as a bird
  Mixture too rich - now purrrfect
  Bag o' cement removed from boot
  Gone on a diet (wife's suggestion)
  Slipping clutch identified as prime suspect

[bmcecosse]

Very good -and as I read it - California Dreaming came on TV on an advert!! Check the clutch adjustment - must be ~ 3/4" free play at the pedal.

[mickeytwonames]

I've just check the odometer against a Sat Nav - the needle wanders about 8 mph faster than she's going and mileage is recorded 1/10 short of the distance. At least now I know. Many thanks all your help.

[rayofleamington]

I would get ~30mpg out of my 948 (less in winter) but could get 42mpg on a long run at 55-60mph.
That was with everything standard and with crossply tyres. The tyres were not well balanced so I didn't often go over 60mph
Having the wheels balanced was low priority as the car was full of filler and fibreglass and is one of only 2 minors I had to euthanise.