Thirsty Moggy

[gtt1951]

My speedometer is showing over on speed, which means it is also clocking up too many miles on the Odometer.
On a known distance trip of 25 miles it recorded 36 miles travelled - a 44% error.
Applying this to the mileage travelled between tank Brim Fills, I'm only doing about 17 miles to the gallon - help!!!
At the end of a "hot" journey, the SU pump was going hell bent for leather, so I thought I must have a fuel line leak. I stopped and popped the bonnet and there were no signs, what-so-ever, of any fuel leaks - so where is it going?
The engine has been tuned using a Gunson's Colour-tune device. The plugs show a healthy light brown deposit and the engine tick-over sounds absolutely fine.
As I have a Series II Traveller, I'm assuming that I have a tank capacity of less than 6.5 gallons . I'm estimating a round trip of about 140 miles to the venue, which means my replacement 1098cc engine will need 2 tank fulls (110.5 miles per fill) to get me there and back!
In the past I owned (and used daily for work) a 1964 Saloon with 1098 engine which also used to take me from London to Northwich (Cheshire), to visit In-Laws, without refuelling (about 210 miles one way).
I reground all the valves and did a head decoke when I got the car last year, fitting a replacement (used, from previous spares holding, with new jet and feed pipe) HS2 carb.
Anyone have any suggestions?

[MarkyB]

Did you replace the needle at the same time?
It would be worth investigating the whole length of the petrol pipe too.
Well worth working out the right TPM speedo for you car and picking on up at the national.

[bmcecosse]

Just because the speed reads high doesn't necessarily mean the miles are also high. You need to check with a sat nav - although you do say a 'known' 25 mile route. Colour tune is useless - you set the idle using your ear....and the little lift pin....... Is the vacuum advance working ? Is it a high comp engine? Plugs should be a light beige - not brown. And check the float level isn't too high causing it to overflow the jet. Also all the usual things - tyres inflated to 30+ psi? Brakes not binding? And - what final drive ratio is in the axle - this could explain the high reading speedo and the miserable fuel economy. It should be a 4.22 - but a 3.9 would be better on a standard engine - and a 3.7 if the engine has been breathed on.

[gtt1951]

Hello BMC and MarkyB,
Some of my speedometer and drive train problems had been discussed in thread viewtopic.php?f=4&t=47894
I believe I have the original speedometer and Diff from when the car had its 803cc engine.
I didn't want to lose the original colour speedo.
I haven't got any fuel leaks,
I didn't replace the needle at the same time as fitting the new jet and pipe kit,
Sparkplugs - for "brown" read "beige" - certainly not "black",
I have been using a Garmin Geko "personal navigator" to show me the speed I'm doing - distance from home to work is a "known" 25 miles exactly. This showed up as 36 miles using the Odometer - unless I had made a subtraction error (will do this run again),
"Jet overflow" - I'm assuming that this overflow would be sucked into the air intake and burned, rather than be pouring out anywhere? Doesn't increase revs.
I haven't done a suction test on the Vacuum Advance - will try this when I get home tonight,
I did set timing and idle by ear, then used the colour-tune to check burn colour, but it was difficult to get it to burn yellow (showing rich), and then backing off to blue.
Tyres inflated to 28 psi, but just changed the back ones (due to sidewall cracking) and it turned out they didn't have tubes in them, although the sidewalls were marked "for tube use" (Dunlop 145x14 made in France) - now fitted 155x14 tubeless but not yet taken on a set distance run - the fronts are still 145x14 (not Dunlop),
The SU pump does gallop after coming to a stop after a long run, with no increase in engine revs, and no signs of leaks.
Brakes not binding as "free-wheeling" unhindered,
Fuel economy could be down to the diff - the previous owner did include a new Diff in the sale which he hoped would sort out the speedo. He hadn't driven it enough to see any poor fuel economy - the speedo readings from his purchase (immediately after an MOT) and my purchase from him, showed about 50 miles difference (as the odometer displays).

[rayofleamington]

the speedo cable pick up, is on the output shaft of the gearbox - basically it measures the speed of the prop shaft.
Changing the diff ratio will give you a speedo error (speed and mileage) - they need to be matched. To a lesser extent, wheel and tyre size also make a difference.
There are companies that will re-ratio your existing speedo (by changing the internal gears) and calibrate it for accurate speed in the same service.

17mpg is terrible however I was regularly getting low 20's on a poorly set up 1098 in commuter traffic, so it's not impossible, albeit quite extreme for a 'small engined, light weight' car!


A few years back I lent my pickup to a guy up north - he was dissapointed with the fuel economy (e.g. on mainly a-roads, mid 30's) until I told him the mileage was out because it had been changed from a 4.55:1 diff to a 3.7:1
His calculation of ~35mpg was actually ~43mpg.

[IslipMinor]

Unless the diff has been changed as well, 36 miles recorded for an actual of 25 seems wrong, even allowing for the combination of speedo, gearbox and rear tyre sizes?

The main difference comes from the different speedo drive ratios on the gearbox tail shaft - it is 4.5 for a Series II 'pudding stirrer' and 2.6 for 948 onwards, then there is a smaller correction from the slightly larger rear tyres.

25 x 4.5/2.6 = 43.3 miles

The tyre size difference is only 2.6% (849 tpm / 872 tpm)

so, 43.3 x 849/872 = 42.2 miles

If you have a 4.55 (std 948) diff, then the displayed mileage will be 42.2 x 4.55/5.375 = 35.7, which is pretty close to the 36 you are getting! Have you checked what ratio it is?

I would think that the speedo you have will show a tpm on the face of 1000, which is the standard Series II. From a looks perspective a standard 948 1504 tpm is identical, gold and 80mph, and will give you good accuracy as well (the larger rear tyres will correct some of the normal 'optimism'!). Sure there will plenty at Charlbury on the weekend?

Then it's just a matter of sorting out the fuel economy. Apart from the obvious of cleaning/gapping the plugs, setting the points and timing the ignition; assuming that the needle is correct for the 1098 engine, adjust it as above for the fastest, smoothest idle and it should be right all across the range (if the correct needle is fitted).

[bmcecosse]

If it's still the final drive for the 803 - then it must be revving away like mad - and that will partly explain the poor mpg. Change it urgently!

[gtt1951]

Islip, I do have a spare 1504 speedo, but it isn't identical as it doesn't have the 1000's IND and BEAM indicators at the top - just has HIGH BEAM in the top middle. I will try it out though, after a thorough clean of the glass and face.
Roy (BMC), the revs are not high when travelling and I only need to lightly press the throttle pedal, but I have noticed, when going uphill, that easing off the throttle gives me better acceleration - could be the Advance control is not working then.

Whatever the Speedo shows (Speed and distance), the Fuel Level indicator goes down too quickly for the distances travelled.

I'll try replacing the piston needle (the refurb kit did come with a Needle Valve, but that was for the float chamber) - I've noted that ESM sell them - but this will be too late for this Saturday. I'll have to carry spare fuel and have a shopping list for the Autojumble.

[IslipMinor]

You can swap the gold faces over, then it will be exactly as it should be! Before you do, is the diff a 4.55? It needs to be for the 1504 (948) speedo to work correctly.

[gtt1951]

That I'm not certain of the current diff - obviously something doesn't work correctly now. I'll have to jack up the rear of the car and do that test someone mentioned, in another thread, about turning the prop shaft and counting wheel revs (or was it the other way round? - have to find the thread).
Or are the Diffs marked externally in some way? Just as well the others in the office can't see what I'm actualy doing at my desk

[IslipMinor]

The diffs can be marked, but not very easy to see under the car.

Jack up ONE wheel and turn the prop shaft until you can see the grease nipple from the side. Mark the wheel/tyre by the ground and turn the wheel slowly TWO complete revolutions, counting the number of turns that the propshaft makes. The number of propshaft turns is the diff ratio!

[gtt1951]

Great, thanks for that Islip - saves me searching the messageboard.
I've also remembered something else. After putting the top of the engine back together again (last November) and prior to taking the car on the road (working on brakes etc), I did have the engine idling for long periods to check water pump, cooling and silt removeal etc., I noted that the fuel level had gone down a bit more than expected, but at the time I put this down to a "sticking" float sender (as a tap with a screwdriver handle would change the indication on the fuel gauge).
Now that I have driven the car, for real, and filled the tank (brim full) twice, I have a real fuel use indication.

It may be that the transmission train has nothing to do with fuel wastage (it certainly has an effect on the speed display and odometer readings).

As the sun has finally come out, I'll dash home shortly (25 miles) and check the ratios - the Moggy is on the driveway at home.

Regards, George.

[MarkyB]

Another thought from another thread too, have you ever changed the air filter?
May not make much difference at tick over but will effect MPG very adversely.

[bmcecosse]

But with black plugs.............

[gtt1951]

Well folks, when I got home, this evening I dived into my Moggy "work clothes" - green work trousers and green shirt, to go with the green car (co-incidental) and a very eventfull evening ensued ...
Jacked the right hand side rear axle and positioned the drive shaft grease nipple at a view point. Marked the tyre and slowly turned the tyre/wheel through 2 revolutions, counting the number of times the nipple passed the view point = 4.25 times.

I then put the car back on the road and, from a designated place, did 2 circuits of a road route (marking down the Odometer reading, at start and finish), then drove off to my local out-of-town Sainsburys to fill up the tank and a "period" Shell 3/- fuel can.
Filled the car and, for the 2nd time, it overflowed! I thought that last time I had been clumsey, but twice in a row means that those stupid narrow-pipe Unleaded fuel hoses don't "kick back" on a full throated Moggy fuel filler - anyone else found this?
So - I wasted a bit of fuel, and placed the nozzle in the Shell can - first pressure of the trigger showed that the blasted can had a microperforation in the base which immediately let the petrol out - so much for buying "period" cans on eBay

On the way out I was being tailgated by some oik in a "modified" car and I broke down (just at the exit traffic lights) - the engine cut out and, as I tried to restart, all the oik, behind, could do was sound his horn (shame I didn't have any of my shotguns with me).
With the bonnet up and the driver's door wide open and me looking under it, the number of car drivers leaving Sainsburys and hooting at me was astonishing (one guy did stop and offer to help) - there was room to my inside/left for cars to pass by and out onto the Dual-carriageway.

The engine wasn't firing and my first thought was "it can't be the coil", which was rather warm! Took off the dizzy cap and did see low tension spark. After a bit of elimination, hit upon the idea that it might be the SU fuel pump - it was, very oxidized points (I'm sure I cleaned them up, or did I only do the 2 spare pumps which, of course were at home).
Did a temporary points clean with a Sainsburys "money off next shop paper voucher" - paper is good for cleaning contacts and the car burst into life on the first starter pull - impressed the helpfull motorist. Got home and did a proper clean.
On Saturady will be carrying spare pumps as well as other bits.

I then went out with my modern car and did one circuit of the test route to get mileage and doubled it up.

I now have another figure to work with - 1.39 Moggy Miles = 1 Peugeot Mile. I'm sorry to say that my previous maths was a load of **!?@ as I worked the percentage error out incorrectly.
The shorter trip showed 5.6 miles as known distance and 7.8 miles as the Moggy goes.
The figure of 16.9 mpg now comes out as more like 27.55mpg - much better, but still a bit low
(144 Moggy miles now equates to 103.6 real miles and NOT 63.6 miles, from previous duff workings).

I made some adjustments to the A/R controls on the DIzzy and did tests with the vacuum pipe, but sucking on it did not make any components move - looks to be a fault here I also did the same test on another old Dizzy - same results, but that one looks a bit rusted up.

To summarize
Speedo = 1000 TPM,
Diff = 4.25:1
Engine & gearbox = 1098cc
MPG = 27.5
Speedo over-run = approx 39%.
Plugs = NOT Black.

As there is only one working day left to the Rally (and a day I have to go to work for), I'll have to go with what I've currently got.

After that what do I have to do to set things right?

See some of you on Saturday, I hope,

George.

[bmcecosse]

The correct final drive for a 948 Minor is 4.55 - with a 1508 speedo. The later 1098 cars had 4.22 final drive (as you have) and should have a 1408 (or thereby) speedo. In both cases they over read by ~ 5% as standard. So - if you intend to stick with that 4.22 final drive - look for a 1408 speedo. If you plan to upgrade to a 3.7 final drive then a 1294 speedo (ex Mini) is EXACTLY correct for speed and miles when using 155 tyres. It would be pretty near for a 3.9 final drive if that is your plan. When you 'break down' - always determine right away if it's a fuel fail - or a spark fail. Saves you working on the wrong system! A good clout on the fuel pump is always worth trying....

[IslipMinor]

Sounds like you have a 4.22 diff using the new Minor and Peugeot comparisons and you get 4.25 turns, so that seems to work OK.

An early 1098 has a gold faced speedo, but it goes up to 90mph. You could mark aluminium disc inside the 1098 head with the needle pointing at, say, 60 mph, switch the face to the Series II, reset the disc to the mark and reposition the needle to 60mph. The odometer will be good for the 4.22 and the speed should be ok for normal out of town speeds. Would be worth checking the whole scale with a GPS to make sure?

Good luck with the economy side.

[gtt1951]

BMC, as always, many thanks for your wise input. As it happens, I do have a spare 1408 speedo, but it has a horrible face and hand and different bulb connectors etc.
So it looks like, whoever had the engine replaced, must have replaced the Diff. If the engine was changed out in 1986, how on earth could the then owners (and subsequent ones) carried on driving this car with such a speedo discrepancy? This means that if I put back an 803 engine and gearbox, it still won't be correct unless I change the Diff.
I think I had better get some sleep time ...

[Deaconbrody]

Hi gtt,

I did the very same thing yesterday when filling up the Moggie. Filling away and the petrol shot out the filler. The thing is you are so used to the pumps cutting out you forget to be careful.

My Moggie has a 1300 Marina engine with a 4.1 ratio diff. My mileage per gallon is all over the place. Averages about 27mpg. I will now be checking it with a portable sat nav after reading this post. I have the original speedo fitted so this will be showing out too. Will check that with the sat nav too.

This is a great post. Always amazed how experienced and knowledgeable the guys are on these forums.

Every day is a learning curve.

All the best,

Ian

[mogbob]

George
No one has raised fuel leakage, as far as I am aware.Have you smelt petrol, either under the bonnet, in the boot or at the back of the car ?

If there is not petrol dripping from a hole, there may be a damp patch / area on the underside of the tank ( if it's still original especially ) where rust is eating away.Damp patch around the union where metal pipe joins the tank ?
What about the condition of the rubber pipe from the fuel pump to carb, is that perished ? Re-inforced pipes are a bit more difficult to inspect but putting your nose "up close and personal " ,will usually identify perished rubber, allowing petrol to evaporate.If it looks perished outside then the internal condition will be worse. Rubber connector pipes for the filler to tank route perished ? Modern fuel " eats " old rubber quite easily.
The metal fuel pipe.. tank to engine bay......not been holed / dented by flying objects ?
It might not be the whole problem but a contributory factor.Whatever ...it's worth eliminating the possibility.
Bob
PS apologises to Marky, just spotted reference to checking fuel line.George it may not be a frequent visible drip of petrol.