Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Fuel Economy

I've been driving my 1500 for a few months now... and I expected better fuel economy than I'm getting. I get about 100 miles out of tank.. I expected double that.

Firstly, what does everyone else get?

Secondly, my thoughts on why are:
1. Idling too high (it is - need to sort that)
2. Too rich (probably)
3. Fuel leak (possible - will be checking perished pipes)
4. Mostly Urban driving

I will fix those (when I get a chance) and then see... but is there anything else I should be wary of?

C L Carter

Not sure how big a 1500 tank is but a 1275 is 6 gallons. Assuming that they are of a similar size that means you are getting circa 17mpg!

With standard 1.25 carbs I was getting 25/30mpg(rural roads).

I've recently switched to a single HIF44 and been told up to 45mpg is possible. I havn't checked this yet as it was not the reason for the change.

Of course, apart from your tuning state it depends how much wellie you give to the pedals.
Gavin Rowles

what you get out of a tank isn't an accurate measure but 100 miles sounds very poor indeed

servicing including tappets, timing and carb set ups should either cure or find your problem

the only other explanation is fuel leak(s)

if you keep on top of servicing, maintenance as per the Driver's Handbook (not manual) and repairs with workshops manuals then you should get lots more mpg and better overall performance of the engine and car overall

ETA: IIRC the original 1500 tanks were a nominal 7 UK gallons so unless the tank has been changed that's about 15 mpg!

Nigel Atkins

sorry meant to also put you'd initially think of the carbs as the cause of such low mpg

unless you've left the handbrake on or something :)
Nigel Atkins

Urban driving ought to be about 30MPG

So how much do you need to put in the tank when you think it is empty. o you only put in 3 or 4 gallons?

The other thing is you must have the ignition timing set correctly and you MUST have a working vac advance! wihout the vac advance working correctly you will lose somewhere in the region of 10 to 20 percent, although that has a biger affect on longer runs.
Robert (Bob) Midget Turbo

What you get to a tank isn't giving us enough info. Fill it to the brim, do a hundred miles in it and then see how much it takes to fill it up again. Then you will know it's MPG with a bit of accuracy.

The reason I say this is that my car had a problem where it started running out of juice after only a hundred miles or so and it turned out to be a broken tank pick up. The tank still had over 2 gallons in it!
John Payne

as John says, you can do it more easily this time of year as much less likely to the fuel 'expand' and spill out because of heat build up

fill right up until the petrol is in the top of the filler tube, have a very accurate measure of the mileage you do then refill in exactly the same way then simply divide the amount of petrol it took to refill to same level into the number of miles travelled

obviously if you're filling up to the absolute limit as I often do the car needs to be parked on level ground and not going up or down big hills shortly after brim full filling

also you want both fill ups to be at roughly the same weather temperature
Nigel Atkins

I used to get 45 mpg on a long run with twin 1 1/2's on an A series.

same run now nets me 61 with the K series. You know it makes sense!!!
Rob Armstrong

Yes, I agree... i've done some calcs based on my last fill up... 16.4 mpg...

Nigel, last time I serviced. I checked tappets for 10thou... is this considered normal for everyone.. or is there a different clearance people use?

I will need check the vac advance... thanks for pointing that out... will also check the timing etc.
C L Carter

There are a bunch of apps for smartphones that make it easier. My Grandfather always had the "petrol book" in his car, and so that's how I learnt to do it.

FuelLog on the Android is the "petrol book" I use now...

I have a complete fuel quantity / miles record of all my cars since 2000; helps me see the benefit of mods/changes; review long-term trends; and spot deviation from norm. It's linked to another spreadsheet that reminds me of service items due.

Anthony Cutler

10 thou sounds close for the tappets. I think they are supposed to be 12, although I cannot see that knocking your fuel consumption so high. Check that your choke is opening properly.

I am currently on a rolling average of 41.7 since I fitted the HIF44, about 3 years/ 18K, ago (keep a fuel spreadsheet) (1275, 5 speed, electronic,....)

Presumably you guys who log your fuel usage see a significant drop in mpg in winter months, perhaps about 10%. It was a surprise finding for me in my wife's Nissan years ago, and I find the same difference applies in my MGB.
Geoff Ev

Worst fuel consumption (other than stuck in traffic) is driving on snow. I think the wheels go round too much.

as an aside, has anyone noticed when filling up that their fuel tanks seem to hold more fuel these days?

in my van, having done 80,000 miles in three years, I get to know within a litre or so how much it will take to brim the tank. most of the time i will out 46-47 litres in, and once on fumes I put 49 litres in. lately when filling up when nowhere near as empty it has taken 48 litres regularly.

I reckon its not my tank growing!
Dan Cusworth

Yes... I graph the tank and average 5-tanks with time, and you can see a very pronounced summer/winter consumptions - around 10% as you say. Also, the Accord Type-R (which I bought nearly new) continued to have improving consumption up to around 100K miles.

Anthony Cutler

C L,
I think Guy is thinking of 1275s for 12 thou

10 thou for 1500 I think unless others with 1500s know better

unless you've made a mistake somewhere 16.4 mpg is very bad, perfect excuse to go for a drive to test consumption

the fuel is either being consumed or leaked (possibly both at carbs)

cables or mechanisms catching or not moving freely, carb floats or needles not working properly, worn or sticking needle(s)

have you adjusted or changed anything thing before noticing low mpg

do you smell petrol

is the generally engine running well

all just thoughts
Nigel Atkins

210 thou for 1500"

Quite possibly correct Nigel.
I don't have a handbook for the 1500 and it is over 12 years since I adjusted the tappets on my car.

12 years? Do you ever drive it? lol
Lawrence Slater

No, I sold it 11 1/2 years ago

some numbers I remember most I don't, neither are relevant to me so not the best for me to remember anyway
Nigel Atkins

yep, the handbook says 10 thou... just checking there weren't any other views on this.

The engine runs well... apart from the 'running on' issue I raised in a different thread.

can't smell petrol

PO said he got 200 miles out of it...

since then... I haven't touched the carbs...

I have replaced some fuel pipe, the two pieces which connect the "balancing bar" to each of the carbs... I have had some the large "T" piece of thick flexi hose (I think breather) when I had the rocker cover off... and I've set the tappet clearances...

I have added dashpot oil... as per the instructions in the handbook...

All service points really... nothing else that I can think off... so not sure why it would change?

C L Carter

Ah, ok, :) Still, no reason not to go round there and do the tappets is there guy. :)
Lawrence Slater

sorry I get confused as there are two of you :)

run-on and low mpg could be connected

you could check clips on petrol pipe you've replaced and those you didn't to make sure there are no leaks

>>the two pieces which connect the "balancing bar" to each of the carbs<< check these are set as they should be and move freely

you could check the fuel bowl floats are not perferated and that needles and seats are not worn or sticking and that the fuel bowls aren't full of crud or tiny grit

I'm not sure when you mean you last adjusted the carbs but you could check them for mixture (subject to tappets and timing being OK or redone

you could take your plugs out and take a photo of them with cylinder numbers (1 nearest rad) before cleaning them, checking gaps and replacing

did you follow the order of first tappets, then points, then timing, carbs last?

Nigel Atkins

I agree with Nigel Atkins' analysis. Low mpg and running-on . . . . almost certainly, the two are related. One of the causes of run-on is a rich mixture. What is the colour of the soot inside the exhaust tail-pipe? After a run, it should be grey, not sooty black.

As Nigel suggests, what I'd do is remove the spark plugs and inspect the colour of the deposit on their electrodes. The colour should resemble that of a buff envelope, medium darkish brownish. If they are black and sooty, then you are running rich. In which case, it's time to investigate the float chambers/valves and carbs. Also, one thing to check is that the carb jets are fully returning home (against the lower adjusting hex nut on the bottom of the carbs) when your choke cable is pushed home. If not, you are obviously permanently running rich.

Andy Hock

Thanks Andy and Nigel... I will venture inside the carbs on Friday... scary.

Anyone have a good way of setting the mixture. My friend Josh is keen on buying a CO meter to do the job from the exhaust pipe backwards... anyone got any experience with these... or anything else for that matter?

C L Carter

I have a CO analyser. Works OK for verifying settings but actually quite unnecessary and I doubt it would help you.

By far the best way is to follow the method intended for SU carbs.
Take a look at the step by step instructions on the Burlen Fuels web site:

Last time I tried to use the SU method, I really couldn't really detect the change when the piston is lifted (listening or using an accurate tach).
I was thinking of getting the Gastester to aid in the process, or last least tune myself to do the proper method!

-- Josh
J Levine

That commonly indicates an air leak around the butterfly spindle.

I am fairly confident there aren't any air leaks (tested with flammable spray), I just lack the finesse required...
J Levine

OK, sorry if that wasn't helpful.
I have a gunsons CO analyser. I bought it thinking that it would take the guesswork out of setting the carbs. But in reality it is a pretty temperamental device and no easier than the old "manual" methods. The analyser probe has to be inserted into the exhaust pipe and allowed to stabilise before taking any measurements. The trouble is the thing doesn't settle down very well. Any slight movement of the probe in the tail pipe and the readings alter so it is difficult to get a steady reading that one can be confident in. Add that if the engine ticks over for more than 3 minutes it needs to be revved to clear gasses through the system and you then start all over again. Well, you get the idea!

That was my experience anyway. Others may have had better luck. I reverted to the "book" way and eventually setting up just seems to suddenly start working as it should.

Use a colortune with twin carbs. A CO2 meter won't help if one carb is out.
R Fowler

Josh, CL,

I hope theses videos might help(?) with the carbs, principles at least,:-

general adjustment, engine not running

general adjustment, engine running

matching pistons

how a SU works part one

how a SU works part two

and of course I’d be derelict in my duty if I mention that carb setting and tuning along with much, much more information is available in the owners/Driver Handbooks :) -
Nigel Atkins

Are you on commission Nigel? Its okay i've already got the Drivers handbook.

I've also seen most of the University Motors stuff... some of it good... some of it not so good. His blackboard explanation of the carbs was very useful.

I'm gonna have a look at the carbs on Friday then. Thanks for the advice chaps

C L Carter

I know you have and I think Josh might have

it's a bit of a standing joke (as well as being exceelent advice) note the smilie

plus others read the thread and may not know such information is in the Handbook or that it even exists

as it happens I am on commision, I've earnt enough this year . . .

to do absolutely nothing

I know I've posted the John Twist stuff before but better twice than not at all and I thought it might be another approach for Josh (he's probably seen them too but same goes better twice than not at all)

whilst doing the carbs check all the other stuff advised in this thread too - good luck

I've probably told you this before too (sorry can't remember as there seems to be 2 C L Caters(?)) so apolgies if I have

to save having to say each time which car you have and your first name, if you want to, you can change your name and location by clicking on to anyone else's 'View vehicle profile', scroll to bottom of that page and follow short, easy instructions
Nigel Atkins

Thanks Nigel... I wasn't having a go! Just being cheeky!

C L Carter

Christian - if you're that nervous, then GET SOMEONE TO HELP YOU!!!!!!! You're not exactly in the middle of nowhere and miles away from anyone and there's lots of people around who are more than willing to help ...

Having said that, the ONLY time that I had such rubbish fuel economy was when some idiot insisted on "doing my carbs for me" and did them incorrectly ..... mind you, things that have been said after that could explain alot!

I'm not being rude when I say that your fuel economy is not only rubbish, but indicative of something wrong in your engine set up, and, even if you have to pay to have it properly set up, you're going to make the money back on fuel quickly enough at this rate ;)

Chris be as cheeky as you like I didn't think you were having a go, I didn't meant my reply appear to be so poo-faced, I should have put in a few smilies perhaps

certainly check for things like as posted before cables ect. and cleaning and visual checks on other stuff

rach I think has a good point, if you had/have a go and you just don't have the knack at the moment get help or I'd even suggest one step further if it's serviced then take it to a good pro and pay for set up and diagnostics, the machine and an experienced pro can pick up difficult to find problems that may not be the cause of this problem but also things like rotor/cap/leads/plugs and carb set up and timing

this will give you a good base to work from in future
Nigel Atkins

For a standard 1275 with nothing skimmed etc what would you expect for mpg? I am getting about 30.

IF a K series is 60 mpg or thereabouts how many miles do you have to break even?
Dave Price

A normal 1275 should be able to do 35/40mpg (dependant on your right foot)

Increase the CR (skim the head) and that should increase (as will power)dependant on the fuel octane used matches CR

With my 1380, 731cam, 11:1CR and 45 delorto (with to big idle jets) I get 30mpg on my easy comute.
And that could be improved with a RR setup and less +5000rpm driving ;)
Onno K

an 'average' of 30 mpg sounds about right but as Onno's put it does depend on a lot of variables a major one of which is the owner/driver
Nigel Atkins

Thanks guys,

Rach I'm not really that scared... (I had the entire back axle off last month just for fun), but the carbs are the kind of thing that I think help would be very much appreciated (especially the first time you do it).

I refuse to take it to a garage for anything. I get carbs... just reluctant to go at a pair of twin SUs of which I have no experience...

I did a mechanical engineering degree! I should just get stuck in =]

Right... 2 more hours of work until the fun starts for Christmas

C L Carter

>>If a K series is 60 mpg or thereabouts how many miles do you have to break even?<<

Depends how much you drive it and how much you paid for the conversion. I reckon mine will have paid for itself in fuel, oil burned and leaked out and Redex additive in about 2 years, or about 12 - 15K miles.

of course assuming the K doesn't result in anything else snapping.

Half way there already!
Rob Armstrong


>>I refuse to take it to a garage for anything.<<
>>I did a mechanical engineering degree!<<

oh no, I’ve got engineer mates they tell me the tensile strength of a fixing explaining why they’re reusing something like a banana shaped screw – they’re just tight bodgers :)

just remember keep it simple, read the manual and check the obvious before getting into degree level stuff :)

how about this then -

I don’t think 60 mpg is an ‘average’ for a K-series and I’m not surprise Rob changed his engine if he had oil burning and leaking and had to use Redex additive :)

even with my sump leak I don’t need to top up my oil between services and don’t need additives for fuel or oil

when the K-series first came out I found for me it would encourage less mpg because of the higher revs with the 16v engine
Nigel Atkins

Not in a midget though was it Nigel :p Powerful engine and a light car is win win win :) :) I don't drive it particularly sedately either, and 60mpg is about average for mine, 50 if I'm ragging it, and 70 if I'm driving it like the granny car the engine came from :p The main issue is that the rev limiter is sooo tempting :)

Equally my A series only leaked a tiny bit, and also only burned a tiny bit, needed the additive to prevent the valve seats recessing. But all those things go together to add up running costs, also the fact that between services on the K series is 12K miles, so that's halved the amount of oil needed right there. And add in the lack of points wearing out etc :p

For reference I got 45mpg from the A series in similar conditions :)

Get stuck in, learn by doing and by making occasional errors and it all works out OK :)
Rob Armstrong

you're right it wasn't an over powerful Rover 214i I first drove with a K-series but they weren't over heavy cars either by today’s standards - they also went in the Caterham as well (and 1.4 IIRC)

I confused with your average as earlier you said
>>I used to get 45 mpg on a long run with twin 1 1/2's on an A series.

same run now nets me 61 with the K series.<<

that's a run not overall 'average' mpg :)

on a run once I got 60 mpg in my Suzuki Cappuccino (the then modern Spridget, same bhp, torque, height, width but even shorter, less boot, but with Jap 3 cylinder, 12 valve, turboed 659cc)

when I had a Westfield 130 (1800 Zetec with a claimed 130 bhp) which was about the same weight as a Spridget and had the 5 gear box it got very good mpg but not 60 mpg

you seem to get excellent mpg perhaps you’re a few stone lighter than I even used to be or your milometer is out or your maths is loose – or you’re an excellent driver in a really well set up car, only way to be sure is for me to passenger with you to see what mpg you can get :)
Nigel Atkins

I think i have worked out why i was getting bad fuel economy.

The front brakes appear to be ON! only a little... but enough to resist free spinning by hand...

As such the discs are a little worn... pads however look okay??

But what to do now? Adjusting them is, I'm sure, straightforward enough. But how did it get like that and how to stop it getting like that again? I must admit I'm very confused... I'd have thought the pads would just wear down until they they had no clearance... which suggests to me it could be a hyrdaulic issue? I have recently replace some rear brake hose and bled the rear system. And the warning light doesn't come on telling me there is a change in pressure between the front and back brakes... so I'm back to being confused about whats causing my brakes to be always on?

Thoughts welcomed.

C L Carter

Front brakes are non adjustable!
If they bind either the caliper MC or flexi hoses have gone.

Warning light?!!? I am not sure about 1500's but non of the 1275 have something like that.
But in any case do not thrust on warning lights on cars notorious for electrical faults!

But I am not sure this is the cause of the fuel economy problem.
If the brakes are on enough to cause problems the pads would realy smel and just glaze over giving verry little resistance.

But a brake overhaul is never a bad thing.
A few tips.

Do everything on both sides (you do not want it pulling to one side)
Do not save on brake parts (the little girl jumping in front will thank you for that)
Onno K

as Onno's suggested plus unlikely but could your discs be slighly warped or are you sure that it is the brakes causing the wheels not to move freely by hand

easy to tell if something is binding the wheels by stopping on a slope and see if the car starts to roll when you take the brakes off and how long it starts to roll and how quickly it builds up
Nigel Atkins

Christian, it may be one of your brake calipers has a siezed piston. I have had this happen to me before. Its qute easy to take off the road wheel and work the pistons in and out - - you will soon find out if one is siezed as you be able to push it back into the caliper. You should be able to spin your road wheel and have it rotate a few times before stopping.

If it was binding on the discs would get very hot and would probably smell as someone mentioned above...

My bet would be with your carbs running rich..

NB I have also foudn the piston lift technique works well enough to tune mixture.. Checking plug colour will confirm if you are too rich... Would be first check if it were me...

good luck!
John Barber


you will soon find out if one is siezed as you WON'T be able to push it back into the caliper. ..

John Barber

If you brake to a halt, still holding the pedal down as you stop, then jack the front up and check if the wheel spins, you will find that it does not! At least not freely at first. There is nothing on these cars to pull the pad away from the disk so you can expect there to be some resistance to spinning the wheel at first. But after a few of revolutions the pad should be "nudged" a bit by the rotating disk, so that although it still makes contact, it doesn't slow the wheel from spinning reasonably freely.

If you think that the pad is still binding too much this may be caused by deterioration in the flexible hose. These break down internally, and then act like a one way valve, allowing the pressure to build, but not to release. A quick check for this ailment is to crack open the bleed nipple on that caliper. If the hose is holding pressure then you will get a spurt of fluid out of the bleed nipple.

The set of three Goodridge s/s covered brakes hoses are supposed to give better pedal feel

if the front brakes are sticking on a traffic free dry wide road with your hands lightly on the steering wheel you should feel the car pull to one or alternate sides under very heavy braking same as if the disc is warped you can usually feel it on the pedal of direct systems but its not always certain
Nigel Atkins

This thread was discussed between 16/12/2011 and 29/12/2011

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.