Ignition timing advance

R

RDS

True Classic
Bear with me through the introduction, the questions are at the end.

UK 1500 carburettor, no vacuum advance, 5 speed engine

Since the introduction of this E10 rubbish I have exclusively used E5 Super or whatever it is called at Shell/BP/Esso (I am told that Esso has no ethanol in it for the moment). I have also reverted to points ignition for the moment.

I have travelled a couple of thousand miles since the last attention to points gap, dwell angle and timing advance and this coincides with my change to Super fuel ie 97 Octane rather than the previous E5 95 Octane.

Given that each type of fuel burns at different rates and does not have the same characteristics as the fuel available when the car was new and the Tech Spec set down, I believe that the advance needs to be increased to allow for the slower burn time for modern fuel.

The published spec for UK 1500 carburettor, no vacuum advance, 5 speed engine is:

55 deg +/- 3 deg dwell

Points gap 0.40 +/-0.03mm

Advance per book is 5 deg btdc at 800-850 rpm idle speed.

I have set the dwell and points gap within spec BUT the performance and running with the advance at 5 deg is very poor.

I had trouble with the timing gun (connections at the ferrite pick up) so set the timing by ear/revs. Later I checked it with the now functioning timing gun and see that at idle I have 20deg advance. It was possible to go further.

There was no kick-back on starting, starting was easy, and driving at over 60 mph (in 4th gear) up a long steep hill did not produce any pinking (that I could hear anyway, but then again, I am poor at discerning sounds) but I am worried about holing a piston or four...

So to the questions: what timing advance are you running with your points 1500 cc engine and chosen fuel?
Have you changed anything since the introduction of E10 in the UK?
What ethanol blend are you using?
Are you and/or your engine happy with the advance?

Thanks
RDS
 
Can't speak to Euro specs as I am in USA, but my USA spec 1500 cc FI car (at a factory spec of 8.5:1, much less compression than Euro cars) really likes more than the 10 degrees of initial advance called for in the factory spec. I am running approx 13 degrees now.

Not because I've ever heard pinging, but for peace of mind with the mild advance I use mid-grade fuel. In the USA our typical octane numbers are: standard at 87, mid-grade at 89, and premium at 93.
 
I have 1500 with factory electronic ignition and run 10-12 degrees of advance at idle with 87 octane gas (US) with no problem. As Dan noted, here in the US we have 8.2 to 1 compression which won't be causing any concerns about detonation. There is a way to read spark plugs to see if you have detonation (pinking) but admit I don't remember the details. I do know if you have little balls of aluminum on your plugs you have a problem!
 
Also keep in mind that US octane ratings are done differently from US ratings ours is a mix of the two systems where in the EU they use just the one.

I find it interesting how concerned many in the UK are over the introduction of alcohol to fuels. These fuels are less prone to detonation and although they do attract more moisture (likely a notable issue in the UK), I don’t see any real issue with them assuming one has replaced the fuel lines with modern alcohol tolerant materials.

Personally I wouldn’t consider going over 15° of advance as that gets you into a lot of advance once all the advance from centrifugal and vacuum is accounted for. Getting much beyond 39° for Hussein on his FI car consistently got him into trouble with even high octane fuels, he was @10.5:1 compression as I recall (my recollection could be faulty).
 
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I run 20 degrees advance at idle as recommended by my cam manufacturer. That required recurving the distributor centrifugal advance to ~32 degrees at 3,000 rpm. Low compression ratio and long cam duration tend to increase advance at idle.
 
I time my 1300 to 10deg, it’s not happy either at 5deg especially after I swapped the cam to a longer duration one. Ideally i’d like to set it at 12~14 deg and as dllubin says this really would need the distributor to be recurved. At the moment I have a bit too much advance at high rpm.
 
I try to use the Esso premium fuel as well, it’s ethanol free depending which part of the UK you are in. Another issue with ethanol other than the rubber lines and corrosion noted above is ethanol weakens the mixture and you may need to up the main jet a half size to compensate, plug colour will give you a clue. This weakening of the mixture causes timing of the fuel and air mixture igniting to vary slightly which can cause higher exhaust temps. This book is a good read and has loads of other information about ethanol fuel.

Classic Engines, Modern Fuel

Classic Engines, Modern Fuel - the website that supports the book. It helps classic vehicle owners understand the problems associated with modern petrol
classicenginesmodernfuel.org.uk classicenginesmodernfuel.org.uk
 
You said you have reverted to a points ignition. I would assume then that you changed the distributor. Do you know the mechanical advance of that unit?

The two relevant data points are; idle advance and full advance. Typically, these engines like to idle at 10+ degrees and want approximately 35~36 degrees to total advance. If there is no vacuum advance then, using the timing light, raise rpm to see how much total advance the distributor is providing and set it at 35~ degrees. Then check the idle advance and see where that is.
 
NEG said:
I time my 1300 to 10deg, it’s not happy either at 5deg especially after I swapped the cam to a longer duration one. Ideally i’d like to set it at 12~14 deg and as dllubin says this really would need the distributor to be recurved. At the moment I have a bit too much advance at high rpm.
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I recurved the original Ducelier distributor in my car. It was not difficult. I found weaker springs to give me the right advance vs rpm, and added a stop to prevent the centrifugal advance from going past ~10 degrees. I have a Bosch distributor that I am tempted to modify to go electronic, but so far the points have never given me any issues.
 
A lot of variables will affect the ideal ignition timing for your specific engine. Not only the mechanical properties of the particular engine build, but things like the climate where it is driven, how it is driven, the cooling system ability to maintain a desired temp, the loads placed on it, fuel quality and AFR, etc, etc. Avoiding detonation is critical. So "more is not always better".



NEG said:
I try to use the Esso premium fuel as well, it’s ethanol free depending which part of the UK you are in. Another issue with ethanol other than the rubber lines and corrosion noted above is ethanol weakens the mixture and you may need to up the main jet a half size to compensate, plug colour will give you a clue. This weakening of the mixture causes timing of the fuel and air mixture igniting to vary slightly which can cause higher exhaust temps. This book is a good read and has loads of other information about ethanol fuel.

Classic Engines, Modern Fuel

Classic Engines, Modern Fuel - the website that supports the book. It helps classic vehicle owners understand the problems associated with modern petrol
classicenginesmodernfuel.org.uk classicenginesmodernfuel.org.uk
Click to expand...
Sorry if this is getting off topic, but speaking of fuel and AFR. And in particular fuels with alcohol added (ethanols). As @NEG says it has more oxygen and therefore equates to a leaner mixture, requiring a change in carb jetting or ECU programming to compensate. This has been a major concern for me; the availability of "E" fuels in my area is very sparse so it would be difficult to consistently get the same fuel with every fill up. Therefore you end up with a constantly changing mixture depending on what fuel(s) happen to be in your tank at any given time. With most modern programmable (standalone) ECUs you can add a "flex fuel sensor" to measure the "E" content and change the ECU settings. But that is getting a bit complex for 40-50 year old hobby cars with archaic engineering and technology. For those living in areas where ethanol fuels are more readily available and with more consistent levels of ethanol content this would not be as much of a problem. As was stated, since the mixture can affect ideal ignition timing, especially when the AFR gets lean, this is not entirely off topic.
 
NEG said:
I try to use the Esso premium fuel as well, it’s ethanol free depending which part of the UK you are in. Another issue with ethanol other than the rubber lines and corrosion noted above is ethanol weakens the mixture and you may need to up the main jet a half size to compensate, plug colour will give you a clue. This weakening of the mixture causes timing of the fuel and air mixture igniting to vary slightly which can cause higher exhaust temps. This book is a good read and has loads of other information about ethanol fuel.

Classic Engines, Modern Fuel

Classic Engines, Modern Fuel - the website that supports the book. It helps classic vehicle owners understand the problems associated with modern petrol
classicenginesmodernfuel.org.uk classicenginesmodernfuel.org.uk
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Always something new to learn around here. Thank you for the link and the info.
 
Back when I was burning fossil fuel I had a 1500 Strada, with among other mods, Merrilli Magneti electronic Dizzy , rally cam, header and compression was slightly bumped sucking fuel through duel Webbers. I would set the timing by the book but was never satisfied so would end up twisting the distributor in the advance direction until it started to sputter the back off a bit until it smoothed out. Put many thousands of trouble free miles on that engine and it ran like a champ even past redline.
 
Many thaks to all who have replied: sorry for the silence but iu didn’t get anyu notifications of any responses.



Interesting re the differing measurement of Octane. I do not have vacuum advance so the situation is initial advance plus centrifugal advance at higher revs. I am not sure at what revs the advance levels off but will have a look when I also check the plugs. Thanks Steve. I will use the dial-back facility on my timing light. Raining today so probably not now.



I have no info on the cam but will assume it is stock factory.



I did increase the main and idle jet size slightly already but will not use the E10 beer that passes for fuel. I take on board what kmead says but he gives it away ref the need to change hoses (which I did two years ago); however the pH of the fuel is different too and is reported to attack metal components too including the solder on metal floats, pumps etc and promotes rust where fuel sits. The motorcycling fraternity are also onto this here.



NEG’s recommended book is indeed good and thanks for the reminder: I forgot that I had seen the articles in the MG Totally T Type 2 online magazine

https://ttypes.org/ttt2/

has downloadable back issues for free and is a great read anyway.



Steve, no I didn’t change the distributor; I replaced the points and condenser with a Powerspark module and then changed back using new and checked condensers on an ASR meter. The Powerspark set up WAS tested in another distributor in a rig I set up and ran for several hours without problem. This was during diagnostics last year when the engine would run for 20 mins only then die and I was trying to ascertain if it were a fuel or ignition problem.



Don: are such calibrated springs available?



Dr Jeff: yes agreed but short of a dyno (destruction) session I will not know for sure. I am looking for a happy medium really. I believe that to set the engine up correctly the order is:

Check emissions equipment is functioning correctly

Set valve timing

Set ignition advance

Set fuelling (carb)



Dragonsgate: yes that is what I have sort of done but backed off a bit all the while keeping my eye on the book specs.
 
RDS said:
Don: are such calibrated springs available?
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I would imagine they would be somewhere. Back in the 70s, before you needed to have a part number to look up on the computer, I went into an auto parts store and told them I was looking for a variety of centrifugal advance springs. The guy went into the back room and brought out an entire drawer with little compartments full of different spring types. I probably came away with about 10 pairs for just a few dollars. I did some experiments to get the advance rate I wanted by testing a few pairs. Then, I set the maximum advance I wanted by making a blocking plate to stop the weights from advancing past a certain point.

Depending on the distributor, you can also try removing one spring to advance more quickly. That works on distributors where the two weights are mechanically linked in their travel so only one spring will limit the travel of both. I would start out by getting the mechanical dimensions of the stock springs and then finding some with the correct dimensions but different spring rates. Weaker springs will give you faster advance, stronger ones will slow the advance.
 
thanks Don and NEG, I will review the plugs asap and keep an eye on the temps, pinking and kick-back on start-up, gather some info then speak to H7H
 
Steve Hoelscher said:
You said you have reverted to a points ignition. I would assume then that you changed the distributor. Do you know the mechanical advance of that unit?

The two relevant data points are; idle advance and full advance. Typically, these engines like to idle at 10+ degrees and want approximately 35~36 degrees to total advance. If there is no vacuum advance then, using the timing light, raise rpm to see how much total advance the distributor is providing and set it at 35~ degrees. Then check the idle advance and see where that is.
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In the Shop Manual, the distributor is shown with vaccum advance diaphragm, which is what I have on my FI 1980. The manual does not show a centrifugal advance mechanism. How does the timing advance work at higher RPM?
 
Hello Alain, the [carb equipped] European Marelli s135 distributor model does not have vacuum advance; the higher rpm advance is set only by the centrifugal mechanical weights and springs. pp 170-171 Haynes Manual refers and demonstrates with pictures.

Given the choice between vacuum and no vacuum advance, I would prefer the vacuum advance in addition, especially when cruising at speed. If anyone wants to donate a vacuum advance s135 distributor, I'd love to test it!
 
S135 (f suffix for X19) doesn't come with a vacuum advance, and early US models had a Ducellier distributor with a vacuum retard mechanism.

If you want Marelli PLEX style electronic ignition for a SOHC with vacuum advance there are plenty of those, lots of Ritmo / Uno / Regata in the UK.

Most performance cars don't worry too much about static advance, they are more concerned about maximum advance at revs, Alfa Romeos for example (but older Ferrari and Lambo are the same) have two marks on the crank pulley, a P and an M

P is Piano (slow in Italian) and you set the idle ignition timing at that mark, but the more important check is the M - Massimo (Maximum) and you hold the engine at 4000rpm and adjust the distributor so the crank pulley mark lines up with the notch in the timing case.

Everything changed when lead went out of the fuel though... leaded fuel burns slower than unleaded (avgas despite being high octane burns slower again) so requires a different amount of ignition advance to combust the fuel / air mixture so as to gain maximum power / efficiency while the piston is still up towards the top of the bore and cylinder pressure is high, if the fuel burns slower and the initial ignition advance (BTDC) isn't sufficient then a lot of energy is wasted due to the piston being too far down the bore to exert full force when the fuel is fully ignited.

The popular belief is that knocking / pinging / detonation occurs when the piston is at or before TDC is a myth, it actually occurs when the piston is around about 2.5 / 3mm or so down the bore on the power stroke, as it's about this point when any unburnt fuel air mix has enough volume and has sufficient space between the piston and head so there is negligible quench effect, the fuel air mix is hotter and can self ignite.

SteveC
 
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RDS said:
Hello Alain, the [carb equipped] European Marelli s135 distributor model does not have vacuum advance; the higher rpm advance is set only by the centrifugal mechanical weights and springs. pp 170-171 Haynes Manual refers and demonstrates with pictures.

Given the choice between vacuum and no vacuum advance, I would prefer the vacuum advance in addition, especially when cruising at speed. If anyone wants to donate a vacuum advance s135 distributor, I'd love to test it!
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Thanks. Mine is fuel injected with a Bosch distributor and vaccum advance.
 
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