Why does my 2.25 demand 40 BTDC static ignition timing?!?!?

Been trying to sort my cousin's 2.25 petrol S3 Hi-cap regarding longstanding ignition oddness.

Last time I borrowed his truck it was horribly thirsty; it does 14mpg tank after tank, carefully checked, wherever I drive it and I'm usually quite a good eco-driver. Good power though and sweet starting. It seemed to want way more static ignition timing than seemed sensible so he bought a new distributor but the same weirdness is there.

I set it static at 10 deg BTDC. Vac advance disconnected and plugged.
She VERY reluctantly deigned to fire up and run. Strobe light agrees we're at 10 deg.
So I swing the dizzy for best engine speed and read off on the strobe...anything from 30 to 40 deg BTDC gives fastest idle!!!
Hmmmm.
I set it at 18 BTDC (lowest advance that gave sweet tickover) and set revs to 590rpm. Swinging the diz to 31BTDC brought revs up to 720rpm, so she really means it. She'll run with 45 to 50 degrees BTDC at those revs with barely an occasional miss.
Test drives on the road at 18BTDC static gave no sign of pinking, and then cautious tests at 25 and now 30BTDC static give absolutely no pinking that I can tell, even at full throttle in top at low revs up a hill.

I assumed a broken first advance spring when she did this on the old dizzy, but this is the same issue now with the new one. The engine actually wants the advance!

Standard points and coil fitted. Dwell is 54degrees; so well in spec. Standard pump petrol in use.

I have tested the strobe against manual static ignition settings at two different speeds with good correlation; it's not a strobe fault.

I developed a technique and laboriously checked the TDC marker was accurate and I trust it at least within a couple of degrees and probably spot on.

Centrifugal advance starts from 1100rpm, is all in at 4000rpm and totals 23 degrees crank, so all about normal.

So how can the engine possibly want such timing?

My only clue is that when setting idle mixture with a Colourtune I happened to notice it seemed bright yellow (very rich mixture) when I slowly opened the thottle to any speed. I suppose a very rich mixture might take a lot longer to burn and so demand much earlier ignition timing??? I fitted a new non-Landrover replacement carburettor (Zenith 36 iv copy) but it still shows this apparently rich mix. Maybe its jetted rich for a 2.5 litre engine (this is a 2.25)? Are individual jets available to experiment? Burlens just seem to do standard repair kits.

It's still the old dizzy cap as I was too lazy to swap the leads over but I can't see that being relevant.

Any clues, people? Where am I being a numpty and missing something?

Actualy it might not be far off, as i was told in an earlier post whilst trying to sort out my electronic ignitions advance curve, the Green book gives a 40deg advance at 4500revs ...
I don't have a fancy strobe light where you can set the advance just a flashing light however having set the static timing at 8deg on the pulley mark and the electronic curve to give me 40 at 4500, it runs fine ...
Could it also be that in your case the timing marks are off or the dizy is 180deg out ...
At least it's running which for some is a bonus right?

Don't forget the vagaries of timing chain and cam skew drive come into it. Many mechanics even the Pro's fail to set these up correctly.
14 MPG is a bit low but you say it is a Hi Cap so maybe on low gearing? A standard 2.25 petrol on normal 4.7 diffs should turn in 16/20 MPG on reasonable journey lengths.

Simon Perks said:

Actualy it might not be far off, as i was told in an earlier post whilst trying to sort out my electronic ignitions advance curve, the Green book gives a 40deg advance at 4500revs ...
I don't have a fancy strobe light where you can set the advance just a flashing light however having set the static timing at 8deg on the pulley mark and the electronic curve to give me 40 at 4500, it runs fine ...
Could it also be that in your case the timing marks are off or the dizy is 180deg out ...
At least it's running which for some is a bonus right?

Click to expand...

Interesting, Simon. I measured the whole curve and although the advance was all in at around 4000rpm, I had 23 deg max advance so with 18deg static I'd be spot on your 40degrees, just 500rpm earlier.
I checked the timing marks, and with number one pot on compression when the points part the rotor arm is pointing at number one spark lead, so the dizzy is in the right place; both good suggestions tho'.
What is your programmable electronic system?

divie said:

Don't forget the vagaries of timing chain and cam skew drive come into it. Many mechanics even the Pro's fail to set these up correctly.
14 MPG is a bit low but you say it is a Hi Cap so maybe on low gearing? A standard 2.25 petrol on normal 4.7 diffs should turn in 16/20 MPG on reasonable journey lengths.

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Ha!!! Just achieved the best instant fuel economy improvement you'd believe on the way back from work. +21.1% just like that! What did I do? Calibrated the odo. I read the trip over 12.8 miles but Google maps says I did 15.5. Plus the latest tank of petrol, over 179 miles, on my new odd ignition timing with the new carb and dizzy gave nearly 10% improvement in mpg. Add in the odo calibration and I'm getting 18.6mpg... which is exactly what you said I'd be getting.
I still worry as over advance can damage an engine. I can't hear pinking but I am listening over a slightly blowing exhaust, gear-stick tizz and the rest of the Series Landrover orchestral sound track.

With the ODO out is the speedo also out by around 25% ? If so you may be running on 3.54 diffs. If you have need to pull a diff out count the teeth. 4.7s have 47 and 10 teeth the 3.54s 46 and 13 teeth. That is if my memory is correct, been many years since I played with diff ratios.

divie said:

With the ODO out is the speedo also out by around 25% ? If so you may be running on 3.54 diffs. If you have need to pull a diff out count the teeth. 4.7s have 47 and 10 teeth the 3.54s 46 and 13 teeth. That is if my memory is correct, been many years since I played with diff ratios.

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Intelligent suggestion, especially as I was coaching my cousin, whose Landy it is, to put the Range Rover diffs on for better economy. 4.7/3.54=1.33 so a tad higher than my correction of 1.211. I think the history of the car would make it unlikely to have been altered. Also, the speedo is out by what it feels like being out by, and varies as you drive, always over-reading by a fair bit but occasionally sticking and swinging. I had assumed this was a fault in the speedo unit but I suddenly have a memory of one of my old cars, MG Midget I think, having a speedo cable gradually fray through and leave a 'fluffy break' so that both ends would turn but there was slippage at the break so that the speedo worked but mysteriously under-read. I'd better throw a new cable in to rule that out. Surely the S3 hi cap had 7.5 tyres from new?

Stevenod said:

Intelligent suggestion, especially as I was coaching my cousin, whose Landy it is, to put the Range Rover diffs on for better economy. 4.7/3.54=1.33 so a tad higher than my correction of 1.211. I think the history of the car would make it unlikely to have been altered. Also, the speedo is out by what it feels like being out by, and varies as you drive, always over-reading by a fair bit but occasionally sticking and swinging. I had assumed this was a fault in the speedo unit but I suddenly have a memory of one of my old cars, MG Midget I think, having a speedo cable gradually fray through and leave a 'fluffy break' so that both ends would turn but there was slippage at the break so that the speedo worked but mysteriously under-read. I'd better throw a new cable in to rule that out. Surely the S3 hi cap had 7.5 tyres from new?

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Do you have a GPS/satnav, a good way to accurately check your Speedo/odometer.
Had this discussion yesterday with my old mate who has just got his 1950 S1 Landy back on the road and is finding the speedo a little vague, though he's more worried about getting caught speeding rather than mpg, I said what! Speeding in an S1, but he's just living in hope I think. Edit, he did say that it really needed a calendar rather than a speedometer!

Stevenod said:

Interesting, Simon. I measured the whole curve and although the advance was all in at around 4000rpm, I had 23 deg max advance so with 18deg static I'd be spot on your 40degrees, just 500rpm earlier.
I checked the timing marks, and with number one pot on compression when the points part the rotor arm is pointing at number one spark lead, so the dizzy is in the right place; both good suggestions tho'.
What is your programmable electronic system?

Click to expand...

Steven,
I am using an ignition system from 123 ... this one
http://www.123ignition.nl/product.phtml?id=30
It has a series of curves that you can select, there is a newer version which has variable settings that you can make via a bluetooth app, this version also has a rev counter in the application.
It has made a big difference to the performance and the fuel consumption.

Simon

I do recall a lot of old vehicles run with very advanced timing, my old BSA was 38 deg. You need more advance if the burn is taking longer which is what happens if the mixing is poor and the combustion chamber shape is inefficient. If you look at modern engines with swirl inlets, injection and squish bands they can set the mixture off later and still get a full burn. I would expect a bit less advance with unleaded as it burns faster but I think that's a black art. Don't forget the geometry, 45 deg is only about 18% of the stroke before TDC (or my maths is wrong, its been a long time)

"Old BSA at 38 degrees" yes that is about right, I run a 1929 BSA Sloper at 35 degrees fully advanced. It would probably be OK at 38 or 39 degrees but the modern fuel makes me use caution.
Stevenod, if you suspect the speedo cable take a look at the speedo drive they are only clamped and can become loose giving the symptoms described.

Gazbo said:

Do you have a GPS/satnav, a good way to accurately check your Speedo/odometer.
Had this discussion yesterday with my old mate who has just got his 1950 S1 Landy back on the road and is finding the speedo a little vague, though he's more worried about getting caught speeding rather than mpg, I said what! Speeding in an S1, but he's just living in hope I think. Edit, he did say that it really needed a calendar rather than a speedometer!

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Yeah, tell him to have his speedo recalibrated back to the original Gregorian Calendar and the device will predict his journey time accurately, right down to the exact week.

I'm a school lab technician so I have a couple of unwanted old 4mm jack-plug sockets from broken physics power packs. I'd like to put those in in place of the fairly useless original dashboard accessory plug sockets then I can use high quality school-type 'banana' plugs to connect a GPS/sat nav, chargers etc. Like your mate I worry a tad for my licence and would like to check what the speedo is telling me.

When I borrowed this truck a year or two back I set the ignition advance by doing timed hill-climbs. I'd find a nice medium hill on a quiet road with somewhere to turn round at top and bottom and suitable road-signs or some such over the main of the steep bit. Then I'd park up, record ignition timing with the strobe, run her up to approach the hill at 40mph in third and gun the throttle and start a stopwatch exactly as I passed the lower road-sign. I'd stop it as I passed the higher road sign, park write it all down reset the ignition timing 5 deg different then do it again. Repeat with different settings until you see the power dropping off on both sides of some ideal timing figure.You can plot a graph of ignition versus hill-climb times (or just eyeball what seem the best figures) then you know by positive test you've set it best for full power. I don't really have time for that exercise now though; it took me a whole afternoon. You have to do 5 or 10 or so runs at the first setting to see how accurate and repeatable your experiment is (otherwise you're just kidding yourself as to what's helping or not), then maybe 3 or 5 at each ignition setting and take the averages. No gear changes allowed; hopelessly variable as is starting from stationary. All a big faff but it would otherwise take an afternoon and £150 to drive to the nearest rolling road to do the job.

divie said:

"Old BSA at 38 degrees" yes that is about right, I run a 1929 BSA Sloper at 35 degrees fully advanced. It would probably be OK at 38 or 39 degrees but the modern fuel makes me use caution.
Stevenod, if you suspect the speedo cable take a look at the speedo drive they are only clamped and can become loose giving the symptoms described.

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I looked up the Sloper; nice! 70-75mph in 1929?!?!? The same cousin as loans me this Landy has a 1932 Koehler-Escoffier 350 bike and I'm sure full advance will be 30 to 40 on that too, but not at start up! Try kicking your 500 cc sloper with the ignition at 35! I can't see how this Landrover runs at high revs with these settings. 35 degrees at tickover plus 23 centrifugal means 58 deg at 4000rpm, plus vac advance at part throttle. I know it's half that advance at the distributor but it must be thinking about firing on the preceding cylinder.

"...take a look at the speedo drive they are only clamped and can become loose giving the symptoms described."

Speedo drive clamp: right, yes, good one, must have a look. Ta!

Is it one where the vacuum is configured to retard. I seem to recall some dizzys were set like that and it may have one of those. I used to have a BSA Gold Star - the mag was weak and the spark was stronger on advance so I'd try to kick it with a bit more advance, one day the invevitable happened and my knee hit my jaw and jarred my teeth loose. Rebuilt the mag after that. Re speedo - I didn't get mine calibrated when it under read by 10% due to 3.54 diffs as I thought £80 was a bit steep so intead I got caught at 33 in a 30 mph and had t cough up £95 on an all day "speed awarenes" course. 3 years ago and I'm still pee'd off about it.

Off topic a bit but yes 500 BSA Sloper is very nice. I also have a 350 which is a whole different bike, only the crankcases are common to the 500. A bit of a rarity as they where only made for 1929/30.

Simon Perks said:

Steven,
I am using an ignition system from 123 ... this one
http://www.123ignition.nl/product.phtml?id=30
It has a series of curves that you can select, there is a newer version which has variable settings that you can make via a bluetooth app, this version also has a rev counter in the application.
It has made a big difference to the performance and the fuel consumption.

Simon

Click to expand...

Hi Simon,
I am about to replace my Lucas dizzy with a 123 Ignition. When reading the installation manual there are 16 curves to choose. I wonder which curve would be the most appropriate one. Is there any advice you can share? My Landy is a 1984 Series 3 2250cc 4 cylinder petrol model. Use 96 Octane or above. Thanks in advance!