Lotus Elan

Elan +2 Ignition Timing

PostPost by: richardy8496 » Mon May 13, 2019 11:32 am

I am trying to time the ignition on my recently purchased 1968 +2. The information in the manual is 10 degrees BTDC static + 14-16 degrees at 2,500 rpm. Unfortunately the rev counter reads about double so it is not easy to get an accurate rev reading. I assume static means with the engine not running - does anyone know what the setting would be at tickover?
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PostPost by: mbell » Mon May 13, 2019 7:46 pm

Should be no advanced at idle, so ~10 degrees.

Sounds like you might have electronic ignition fitted. If so you might be able to improve your rev counter accuracy by moving the 12v power supply away from the coil 12v supply. This is because the tacho work by sensing current pulses into the coil, if your electronic ignition module gets power from the coil it is also creating current pulses that the tacho can pick up meaning double or strange readings.

The full solution to this is to upgrade the tacho to a RVC setup but that not as simple as moving one 12v connection....
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PostPost by: richardy8496 » Tue May 14, 2019 12:37 pm

Thanks very much. I am not sure if the ignition is electronic - certainly the coil and leads have been uprated so possibly it is, but I can't get at the distributor without removeing one of the carbs. I understand the coil feed to the tacho but what is the 12v power supply cable?
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PostPost by: wotsisname » Tue May 14, 2019 12:57 pm

with suitably wibbly fingers you should be able to get to the clips that secure the distributor cap and look to see if the points are still fitted. Another telltale can be the number of wires leading to the distributor from the coil, for example an Aldon ignitor has a red and a black wire fro mteh two sides of teh coil to the distributor
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PostPost by: richardy8496 » Tue May 14, 2019 4:22 pm

Thanks, Adrian. Had a fiddle and managed to get the cap off (Lucas distributor with 2 screws holding the cap on) but it looks like a conventional set up with points and condenser.
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PostPost by: rgh0 » Wed May 15, 2019 9:47 am

richardy8496 wrote:Thanks, Adrian. Had a fiddle and managed to get the cap off (Lucas distributor with 2 screws holding the cap on) but it looks like a conventional set up with points and condenser.
Richard


It sounds like you have a later model replacement distributor as the standard distributor always used clips to secure the cap. If thats the case your advance could be anything.

A standard road Twin cam on webers needs around 10 to 12 degrees crankshaft advance both static and at idle speed with the centrifugal advance starting about 1000 rpm and going to a maximum of around 28 degrees combined static plus centrifugal advance above around 4000 rpm.

The exact details depend on the specification of the engine as Lotus changed the curve over the years. The details are covered in the workshop manual but Lotus made errors mixing up distributor degrees and revs with crank degrees and revs in the numbers they quote.

Many modern timing lights have a digital tacho built in to their display so you can use that to set and check the timing versus the sometimes inaccurate Tacho in the dash with its 50 year old analogue electronics

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PostPost by: JonB » Wed May 15, 2019 1:17 pm

Hi Rohan

In the UK we use Unleaded 95 fuel that often contains some ethanol. Does this need a different advance setting to what is in the manual in your view?

Thanks
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PostPost by: rgh0 » Wed May 15, 2019 2:57 pm

JonB wrote:Hi Rohan

In the UK we use Unleaded 95 fuel that often contains some ethanol. Does this need a different advance setting to what is in the manual in your view?

Thanks
JonB


Ethanol burns slower, so its addition boosts the octane rating. High Octane rating slower burn, low Octane rating faster burn. If anything running a 95 Octane ethanol blend fuel would require a little less ignition advance than a 98 Octane premium unleaded fuel. However the difference would be small and whats the right setting would depend on a lot of other engine variables so unless you put it on a dyno having the right advance curve for modern fuels is pot luck.

Having said that ... most of the standard Lotus advance curves are pretty conservative to what the standard engines will actually take so unless you have radically changed cams or compression ratio the standard Lotus curve should work OK on 95 Octane 10% ethanol blend.

The biggest issue with modern fuels is lower vapour pressure to reduce evaporative emissions and fuel injection engines are much less sensitive to vapour pressure of the fuel especially when cold compared to something like the Elan with its 4 Weber chokes. Poor running of Carb cars on modern fuels especially when cold is principally due to this in my opinion.

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PostPost by: JonB » Wed May 15, 2019 4:27 pm

Thanks Rohan! I will give it a go at 10 degrees static BTDC, I think - it is set at the proper 12 degrees at the moment, assuming the marks on my cam cover are accurate (which I doubt after reading a few timing threads).
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PostPost by: 69S4 » Thu May 16, 2019 6:01 am

I wondered how accurate the pulley marks were when trying to sort out my high idle speed recently (still not solved) and checked with a dial gauge down a plug hole to find tdc. They were spot on, with the pulley notch exactly level with the tdc mark on the front cover.
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PostPost by: chickenstock10k » Fri May 17, 2019 1:50 pm

JonB, can you share a little more info on the engine setup and distributor? Do you know what kind of distributor you have? Do you see a vacuum retard pod on the dizzy?

On the tach question, there are a bunch of cheap timing lights that have a built in digital tach on them, which I have found very helpful. My analog tach reads about 100 rpm too high, which made dialing in idle a pain.
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PostPost by: JonB » Fri May 17, 2019 8:25 pm

Standard dizzy 23 D4 41189E for the UK Big Valve engine, no vacuum advance. Engine was rebuilt by QED in 1992 but I have not had it apart to see if any special cams were fitted. Goes like the clappers, though, and revs all the way to 7000 RPM.

Regarding setting the timing, engine speed doesn't matter so much at tick over (750 RPM) as it is below the point where the centrifugal advance kicks in (. I agree for testing at higher revs it matters.

There's a thread I started to discuss it a while ago: viewtopic.php?f=39&t=40971

Interestingly I had an issue with bad running and the timing was spot on. It went away after 10 miles or so - I wonder if the carbs are playing up. Anyway, apologies to the OP I seem to have hijacked his thread!
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PostPost by: chickenstock10k » Fri May 17, 2019 8:45 pm

As an FYI, those were all vacuum retard, not advance, which is a bit confusing.

So, I would be careful about assuming that the advance isn't kicking in at idle. While the manual isn't clear on this, I've seen a couple of degrees come in between 500 and 1k. Food for though.
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PostPost by: JonB » Sun May 19, 2019 3:17 pm

chickenstock10k wrote:As an FYI, those were all vacuum retard, not advance, which is a bit confusing.


Interesting..

chickenstock10k wrote:So, I would be careful about assuming that the advance isn't kicking in at idle. While the manual isn't clear on this, I've seen a couple of degrees come in between 500 and 1k. Food for though.


What car did you see this on?

According to Miles Wilkins, my advance curve is static to 2000 RPM then you get advance up to 26 degrees at 5000 RPM. So on my car, at idle (or rather anything less than 2000 RPM), I should see 12 degrees advance at 750 RPM tickover (the static advance figure) unless I'm really doing 2000 RPM or my distributor is faulty or has incorrect weights / springs.

If you are talking about the Lotus Workshop Manual, my copy does not list the timing figures for the Big Valve / Dellorto equipped engine (it gives Weber at 10 degrees static, which - again according to Miles - is the non big valve engine with 41189A dizzy).

As to confusion, I can definitely agree with you there. It's a bit of a minefield, until you identify what engine / dizzy / cams you have, and have got your head round the various publications.
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PostPost by: chickenstock10k » Sun May 19, 2019 5:31 pm

So, I'd say that I got this information from my own experiences, so your milage may vary.

That said, when I upgrade to an equivalent "stock" dizzy from petronix (ignitor ii), I actually asked them for the exact advance curve from 0 BTDC through the end of the advance. It is as follows.

RPM Degrees Advance
600 - 2
710 - 4
820 - 6
940 - 8
1100 - 10
1300 - 12
1550 - 14
1780 - 16
1900 - 18
2300 - 20
2610 - 22
2050 - 24
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