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MG Midget and Sprite Technical - for those who love good curves -CSI

I made a thread a few day's ago reg. why I have to go with ABH and not the AAC needles recommended for a 1971 CJ engine.
What suddenly came to my mind is, that when I had to switch from AAC to ABH needles, must be when I fitted an CSI ignition in June 2017.
I'm not 100% sure, but I think the old worn out Lucas dizzy was a 25D4. According to CSI, I should choose curve number 7, so I did. But maybe my engine would like another curve, maybe it's what causes that I have to drive with ABH needles. They have a richer mixture at speed - likely in the 2000 - 2300rpm range ??
The engine was originally an American LC engine that I gave some HC 21253 pistons. All the emission crap is gone and everything blanked off, I believe it to be completely "Europanised".
Any experience here with CSI and which curves do you use?
Do any of you see a curve more suitable for my stock engine on the attached sheet?
Can a wrong curve = wrong advance cause the need for more fuel - richer mixture?
Apart from all the written words I have to admit that the engine runs quite smooth, only, why not with AAC needles anymore...?
I have attached a sheet presenting the curves, for some reason the sheet turns clockwise when uploading, I don't know why.



Jan Kruber

smaller but saves twisted neck



Nigel Atkins

Not the sort of curves I was expecting :o(
Dave O'Neill 2

Jan
Other things come into play with mixture as well
The usual mods that lean the mixture off are free flowing air filters and larger free flowing exhausts
If you have either or both of these--it could be the cause of needing a needle change
willy
William Revit

Willy
It's hard not to keep this message short, sorry:
Everything is stock, apart from the dizzy. I believe I can compare the engine with the European engines build at the time.
When I bought the ex US car nearly 2 years ago it was very original. There came a whole compilation folder with the car with history from about 1991 and on, where it was sold to Denmark and regisrered in 2007.
The Californian guy who owned it before it was shipped to Denmark, spended in the range of £6000 in the 15-16 years ownership.
When I took over the ownership I gave the engine an internal inspection, looked quite good, gave it new shells as I was there and some 21253 (9,3 CR ?) pistons and removed all the US non emission equipment and blanked off all that had to.
What was most worn out in fact was the rocker shaft, fitted a new assembly and had the head looked after, skimmed and valves regrinded and new oil guide seals.
When starting up the 2017 season, the first midget season ever for me, I had to run in the engine for about 500 mls, and I don't recall having had the issue with the lean running in the period. Allthough not absolutely 100% sure, I believe it started when fitting the new ignition. With the AAC needles, when having a nice idle, it would run a little lean at speed, that could very well match the 2000-2300rpm range, where the advance curve makes an increase in advance. Why do I think it ran lean; because when pulling the choke a little it would run soo smooth. I found, on the internet, a manual jow to find the right SU needle which describes the procedure. They mention, that when experince what I did, pulling the choke, I would have to find a needle with a richer mix at that speed /rpms. That's the ABH needles.
All that said, I wrote to CSI the other day, they surely has a lot of experience, producing, selling and supporting those CSI's.
And, when having the time, I can take a journey and try the differen turves, it's easy to switch between them, it only requires a smal Philips screw driver.
I think I can exclude the curves 13 to 16 since they advance up to 40 degrees, right?
Jan
Jan Kruber

Jan,
I can't remember, is your exhaust system standard to original or standard to "Europeanised" or non-standard (perhaps single box instead of double boxes)?

Which needles are standard to original and which standard to "Europeanised"?


I'll put a small bet CSI suggest you contact one of their dealers or Swiftune for the info you want - but - I know nothing about CSI or their history, they appear to me to be Mini centred, their website has a Netherlands registration same as 123ignition has, a coincidence or not I don't know.
Nigel Atkins

Jan

Curves 5-8 are the best choice for your engine

Curves 1-4 would best suit high compression modified engines
Curves 9-16 have way too much advance for your engine

Just looking at the suitable curves 5-8 I'd say 5 and 6 are too slow getting advance
Even the 7 is a bit retarded around that 2000 rpm mark so I think your best choice would be No8
Running with the timing retarded from optimum results in the driver having to have the throttle pushed down further to maintain road speed and the engine would run hotter/leaner
Trying No8 curve might just be enough to fix it------keep an ear open for pinging at that speed though just in case it's too much-
Should be right though- A std dizzy set on 10deg idle would have around 26-28 d. at 2000
Where the No8 still only has 22-23 at 2000
If 8 is ok you could try bumping the initial timing up from 10 to 12 for a try which would bring the 2000 rpm up to 24-25 which is really close to std spec at that speed-
Does your dist. have vac. advance
Have fun
willy
William Revit

I often think that there are far far too mnay variables in play for this to be an presciptive science. My simple advice is therefore to take a trial and error approach. Fiddle with something, if it improves things then fine, if not, take it back to what it was and adjust something else. That or take it to a rolling road.
Oggers

Jan,
whilst looking for something else I found Peter Blockley’s spreadsheet for needles -
https://www.dropbox.com/s/zt7k98ryfwwd3g1/SU%20Needle%20chart.xls


Nigel Atkins

Nigel
According to the my SU "bible" the 1970 and 1972 Midgets in US had AAC or ABC, for some rason the 1971 range is not at all menyioned. Aææ other Midgets in 1971 ran with AN (fixed needles) or AAT (spring loaded)
I really miss the online mintylamp comparision table.....
Thank's for the needle chart
Jan Kruber

William
This is very informative. Last year I found a table on the internet with recommended curves for the spridgets, but I can't find it anymore, so you saved me, great!
Looking forward to test :-)
Yes, the dizzy has a vac. advance
Jan
Jan Kruber

Jan,
no, no, no, I can't think after all this time you could mix up what is the good book!

Lucky for you I fund my electronic version -
Midget MKIII NAS Driver's Handbook.

And I quote from General Data, Page 51 -
"Carburetter needle
12V - AAT (spring loaded)
12CJ - AAC (spring loaded)
12CD - AN"

This amalgamated paper print copy of the US Editions shows as published in 1971 covering (model years?) 1967-1972 so should cover your model -
http://brooklandsbooks.co.uk/index.php?route=product/product&path=12_138_631&product_id=561

Never let us speak of the SU book other than by that appellation.

Nigel Atkins

Nigel
Oh...great, that little handbook is allready in my possession, came with the car......and my engine is the CJ....
Thanks Nigel
Jan Kruber

Jan,
you have to meet the maker(s) half way, they provide the good book you have to read it and refer to it (frequently). :)
Nigel Atkins

Willy
Today I took a spin and with the engine at working temperatur I gave it curve No 8. It is marginal, but I think it was for the better, It was not worse, at least. At the same time I felt that it was running marginally richer in the rpm range we are talking about. But again, marginally, maybe it's imagination...?
I then gave it curve no 6, this was worse, here I'm not in doubt.
So maybe you guided me on the track. Does this increase in advance mean that I could maybe choose a needle with a leaner mixture at the rpm range we are talking? The AAC maybe?
Jan
Jan Kruber

I have the CSI on my standard 1275 midget- it is on curve 4 and seems fine to me, I will have dig around and try to recall why I used that curve, I am sure it was based on someone's advice.

Really excellent support from CSI - same day replies to emails - it might be worth asking them?

Mike
Mike Dixon

Jan
Maybe
How are you measuring the mixture
The only real way to know is with a gas analyzer when it gets down to finer udjustment
If you are going by plug colour, you have to realise that cruising mixture is usually leaner than full power and the plugs will go lighter
Maybe try the AAC's again and use the choke method to see if they are still too lean
Also make sure your car is nice and warm when you agjust the idle mixture as this adjustment carries right through the range
William Revit

Willy
I had a second thought, please correct me if I'm wrong:
If an ignition is too far advanced, the burning will be leaner, right? If I am right in stat statement, the lean burning in the 2000-2500 rpm area with the AAC needles could indicate that the ignition in fact is to far advanced in that area. I propably cured it wih a richer mixture by fitting ABH needles.
You suggest I go to curve no8, which is a few degrees further advanced than no7. But maybe I should have gono back to curve no6, a few degrees retarded compared to no7. That should then give a richer burning with the ABH needles, and maybe I then could go with the AAC needles again?
Do you understand my rubbish, English is clearly not my mother language.....
Jan
Jan Kruber

Mike
I have written to Wim at CSI and explained the issue, haven't heard anything from him yet. Last year he replied instantly, maybe he's on vacation....
I thought about curve 6 in combination with the leaner needle AAC maybe......
Jan
Jan Kruber

You need to bear in mind modern fuels in no way resemble the chemical composition of old four star petrol available in 1970, or their burn characteristics. Your best bet would be to keep the ABH needles and take it to a rolling road. In that way you'll end up with the best advance curve together with the right needle profile - from a series of measurable improvements. Anything else will be guesswork.
f pollock

Fergus,
IIRC the CSI curves allow for modern petrol.

Which modern petrols I don't know, probably the overall composition, I've no idea how much petrols vary in different counties and how much that needs to be allowed for or not. I put this to show my level of ignorance.

I hesitate suggesting a rolling road tune-up other than with Peter Burgess as I know from long personal experience that the quality of these can vary, this I do know for certain. Of course there are other good rolling road tuners out there but you want one experienced and good at setting up Midgets and the like.
Nigel Atkins

At this stage Ferg.s suggestion of a roller tune would probably be best, and keeping the ABH as well till then
How much ethanol is in your fuel there---??
You asked
"If an ignition is too far advanced, the burning will be leaner, right?"

If the ignition is too far advanced it creates extra heat in the combustion chamber and can cause pinging(detonation) It won't cause a lean mixture-BUT a lean mixture itself can also cause extra heat, pinging etc
Richening the mixture can mask other issues like timing
You need to get a gas analyser hooked up on it to get the mixture sorted properly otherwise you will be going for roadtests forever

willy
William Revit

Vim Weldkamp from CSI has replied my question:
"When fitting the CSI richer mixture is normal, because the burning speed of the petrol is better than with a points dizzy. Curve 7 or 8 will do, I use curve 8 for my MGB"
As mention in the premilinary thread the engine runs smooth, and I have been driving with the setup for more than a year. I thread was actually just started because I wondered why I had to go to richer needles. The marginally rich burning that I feel at +/- 2000 rpms might be imagination, because when looking at the spark plugs after some idle, some running at 2000 rpms and after some full throttle, they are all the time light brown / brown, so no indication at all that it should run too rich.
I will carry enjoying riding the little Midget with curve 7 or 8
Jan
Jan Kruber

Jan
Thanks for the feedback--
Just for interests sake, because you have plenty of spark, it might be worth opening the plug gaps out to say 35thou. for a try to see if it runs better/smoother at that 2000rpm cruising point

willy
William Revit

Willy,
with my Midget, 123ingnition fully electronic dissy and the set up I have, on Peter Burgess's rollers we discovered it was best to run at 28thou (we also discovered that I didn't know how to use a feeler gauge properly but that's another matter).

I'd previously got the gap at my loose interpretation of 0.8mm (metric wire gauge) so probably close to 35thou even though I intended less.
Nigel Atkins

Jan,
my apologies to Vim Weldkamp of CSI for thinking they'd redirect your inquiry elsewhere.

I must admit the response used to be very indirect from 123.
Nigel Atkins

Nigel--if Peter ended up with 28 then that must be best - I just thought the extra gap might help on light throttle - just for a try out of interest
William Revit

Willy,
just a comment referring to my car. I thought the same and have previously run at 30ish-35ish with reasonable results on the rollers just that as Peter had found 28 good for Bs and my settings were sloppy we thought we'd try my sloppy settings, 25 and 28 on my Midget as a comparison.

There wasn't much difference and IIRC the 28 was slightly less output but better overall, I don't take too much notice of the actual numbers and look more at the graph line patterns, not that I understand very much of it.
Nigel Atkins

This thread was discussed between 01/09/2018 and 06/09/2018

MG Midget and Sprite Technical index

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