Lotus Elan

Ignition Advance

PostPost by: vincereynard » Sat Jan 13, 2018 1:00 pm

I have been checking the ignition advance with a new strobe kindly bought by Mrs R

screenshot-from-2018-01-13-12-53-22.png and


Irritatingly it starts at 10 degrees so has to be reset to 0 every time.
Usefully it is nice and bright and has a revcounter.
This shows the timing as :-

700 revs = 9/10
1000 revs = 12
1200 revs = 18
1500 revs = 20 / 21
2000 revs = 28 / 29
2500 revs = 28 / 29

I'm guessing I could advance a couple of degrees static but does that curve sound about right for a BV Twink?
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PostPost by: MarkDa » Sat Jan 13, 2018 2:58 pm

Vince
I think that the short answer is No - the curve isn't quite right.
Tickover is 12° and then linear to max of 26° at 2500 rpm.

The max advance is stamped inside the distributor.
What dizzie do you have?

Not a new subject of course, here's a thread with a good explanatory link in the first post.

lotus-electrical-f38/tuning-lucas-distributor-t28918.html

Mark
Last edited by MarkDa on Sat Jan 13, 2018 6:31 pm, edited 1 time in total.
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PostPost by: vincereynard » Sat Jan 13, 2018 5:42 pm

MarkDa wrote:Vince
I think that the short answer is No - the curve isn't quite right.
Tickover is 12° and then linear to max of 26° at 2500 rpm.
The max advance is stamped inside the distributor.
What dizzie do you have?
Mark


Thanks for that. Close enough for now.
The dizzie is an accuspark replacement with electronic trickery installer. Not an original Lucas. However it seems well made with no measurable slop in the bearings. Not that Lucas was the last word in quality.
I shall investigate sourcing new springs and see if it makes any difference.


MarkDa wrote:Not a new subject of course, here's a thread with a good explanatory dog in the first post.
Mark


Is anything? :) Thanks for the point towards the reports.

Vince
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PostPost by: MarkDa » Sat Jan 13, 2018 6:15 pm

Vince
I got the impression that accuspark didn't match twink curves?
Mark
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PostPost by: vincereynard » Sat Jan 13, 2018 6:31 pm

It was supplied and fitted by Spyder - say n'more!

As I said it seems well made and gives a good steady spark, (no noticeable scatter), so it will do for now. A rolling road is scheduled anyway. Lucas could have been + / - a fair bit anyway.
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PostPost by: MarkDa » Sat Jan 13, 2018 6:54 pm

Spyder may have fitted different springs?
I was rather surprised to see how simple the are really with a max stop and a couple of springs to mix and match.

You were quick on those doughnuts!
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PostPost by: vincereynard » Sat Jan 13, 2018 7:14 pm

MarkDa wrote:You were quick on those doughnuts!


I had to be, Marge may have been watching!
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PostPost by: Spyder fan » Sat Jan 13, 2018 7:47 pm

Did somebody mention donuts?

Image

Vince, you could be the new Grumpy! You have all the necessary attributes for the position 8)
Kindest regards

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PostPost by: rgh0 » Sat Jan 13, 2018 10:10 pm

The curve is way off assuming you are talking in crank rpm, as it looks like Spyder may have have fallen victim to the error in the manual where the advance curve is quoted in crank shaft RPM when they really mean distributor rpm.

You should have around 10 to 12 crank degrees static advance and it then linearly increasing to around 26 to 28 crank degrees at around 5000 rpm.

Depending on fuel, compression ratio and cams that advance can be a little more and come to its maximum a little earlier.

Assuming you have a steady state brake dyno and not an acceleration dyno which most rolling road dyno unfortunately are these days you can hold the car under maximum load at 1000 rpm intervals and adjust the advance for maximum torque / power at that speed to determine the curve for your engine and fuel

cheers
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PostPost by: Craven » Sat Jan 13, 2018 10:47 pm

This available from Accuspark web site.

s-l640.jpg and
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PostPost by: MarkDa » Sat Jan 13, 2018 11:10 pm

Thanks Rohan I had forgotten that the rpm quoted in the table I was looking at was for the crank.
Vince was quoting engine rpm I think,
so his advance was far too quick.
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PostPost by: vincereynard » Sat Jan 13, 2018 11:58 pm

rgh0 wrote:The curve is way off assuming you are talking in crank rpm, as it looks like Spyder may have have fallen victim to the error in the manual where the advance curve is quoted in crank shaft RPM when they really mean distributor rpm.
cheers
Rohan


I doubt Spyder altered the distributor Rohan. Just source it and stuck it in. The fact they managed to get it the right way up is a definite victory in itself.

So what you are saying is the manual is wrong? Tech. Data page 14 shows a steady increase from 2.5 @ 1250 revs to 14 at 2500, both + static. But this refers to layshaft / distributor revs not crank? Therefore with 10 degrees static, maximum advance would be 24 at 5000 crank revs?
That would explain the huge difference between Page 14 and Page 15! I thought it was strange.
My advance is no where near! Springs / weight or just a duff dissie?

I'll have a chat with Accuspark. First I'll have another try with the strobe to see if a second run gives the same results. The strobe instructions are Martian.

Thanks for the accuspark test data Craven, I'm glad I asked now.

It makes ione wonder how many of the originals were anyway near correct?

Vince

Alan, I suspect the position would better suit one of your err. fuller figure.
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PostPost by: rgh0 » Sun Jan 14, 2018 4:14 am

Yes the data in the manual on page 15 for the 40953 dizzy is correct.

The data in the manual on page 14 for the 41189A and 41225A and 41225 is incorrect as the scale of 1000 rpm to 2500 rpm in the table that is labelled as "crankshaft rpm" is actually "distributor rpm"
i.e. The table should go from 2000 to 5000 crankshaft rpm for the advance figures quoted


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PostPost by: vincereynard » Sun Jan 14, 2018 10:48 pm

Mind you it does not feel over advanced. Although I'm still being gentle, it trundled along, at 2000, behind a cyclist for a mile or so down a twisty lane without stumbling and pulled cleanly away without pinking. Full throttle from 3000 - no trouble or hesitation.

So, I'm guessing, the ignition and carbs. cannot be that far out? Starts on the button with the electric pump. (Tempting fate?)

The only small problem so far it the throttle sticks a bit and wont full close. So it has a tendency to
idle at 1000 > 1200.
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PostPost by: JonB » Mon Jan 15, 2018 6:53 am

Would a new throttle cable be in your near future, Vince? Mine was worn and incorrectly fitted. I'd oiled it (small improvement) then realised it was fitted wrong so corrected it. Much better - then it snapped while I was testing it (in the garage thank god).
1973 Elan Plus 2S 130/5 - UK - Chassis 50/1115L
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