MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Needle Choice - Starting Point

Firstly, hello again to all of you, I've not posted on here for a few years as the arrival of three children over the last 10 years has kept me busy. Thankfully I was able to keep my car under wraps in the garage and I made the effort to keep it Mot'd and running, although I've not really been using it.

Onto my question; I have a pretty much standard 1974 1275cc midget, I have fitted a Maniflow Medium-Bore Manifold and Single Box Exhaust system along with K&N Filters, I have changed the Needles from 'AAC' (Standard) to both 'AAN' and 'AAQ' types as suggested in the Moss Tuning Catalogue but the car never seems to run well on them.

I have an old Excel based Needle comparison chart and when I put the various Needle Specs into the chart it shows the supposedly 'Richer' Needles as actually being 'Leaner'. I have attached a couple of pictures that I hope show what I mean.

So, is anyone running a similar set-up to me, and would you care to share what Needles you are using. I know to really get the best out of the set-up I need to get a rolling-road tune-up arranged, but I was hoping there might be a better starting point than just using the standard 'AAC' Needle as I am at the moment.


Thanks for reading,

Tim.






T Holdsworth

Tim,

it might be easier and quicker to take your car to Peter Burgess and get the right set up first time. Not sure if or how he's operating at present so maybe worth dropping him an email to find out.
Mine's similar to yours with mainly a standard set up, an RC40 and LCB but with standard air filters and Peter did a great job of setting it up. It flew home!
Jeremy MkIII

I’m in a similar position, 1500 with new Maniflow LCB and Maniflow side exhaust system and K&N filters. I’m still on the same standard needles, well that’s what I assume they are, I haven’t actually checked. I have also had the head skimmed to cure a leak so the compression ratio has increased a fraction.

I’m on the 123 ignition, 10 deg static and 22 dynamic.

When cold with the engine on choke it runs like a dog with the odd backfire on acceleration. No sign of pinking though. Once warmed up it runs great with noticeably more power than before.

I’m going to select a curve with slightly less dynamic advance to see if it cures the backfire, and get the car on a rolling road at some point soon.
Chris Madge

My set up is pretty similar to yours and having tried the same needles as you and probably a few others that I can't remember, I also ended up with the standard AAC with blue springs as being best suited to my driving style.

From the residue on the exhaust tail pipe, I think it runs a little rich but I'd rather that than too lean. (AAN)

My notes from ten years back tell me that AAZ + red springs also ran well but at the time I was running a noisy Peco exhaust, now changed to Maniflow.

I've seen AH2 + red springs recommended (Vizard: Cooper S rich) but I haven't tried that combination.

It's never been tested on a rolling road as I'm happy with it as it is.
Peter Blockley

Another one in a similar position - sorry no help Tim!

Mines a 1275, PB Econotune head, 254 Cam, 10:1CR, 3:1 Manifold, STD ignition, carbs + filters. Running on standard 1275 needles (well whatever came in the std rebuild kit!) and it runs quite nicely though the plugs do look a bit too light. Only done 150 miles with it so need to get it well run in before a trip to Peter for setting up.

If you are sure it’s running lean you can always try to modify a pair of needles to see if you can get it running better until you get it to a RR.

Isn’t there a needle selection program called Winsu that you can download?
John Payne

Your chart is correct
AAN is way too lean
AAQ is a bit richer than AAC (std)down low and mid range and then tapers off to about the same as AAC on full hook
AAQ should be very close, close enough to drive till you get it on the rollers

If it's not running right and the aircleaners are new, maybe they might be over oiled or the filters or gaskets not lined up with the holes on the face of the carburettor for the vents for the suction chambers---you could give it a run with the AAQ needles and no air filters to see if it's a filter issue

I've had a bit of luck with ABQ needles with K@Ns and free flowing exhaust on a 1275 mini which was otherwise std and just checked it against your AAQ and it's very similar to them apart from the ABQ keeps the mixture richer right through the range
--might be worth a try-- if you can't find an issue with the filters

willy
William Revit

Stealing Willy's thoughts.

I over oiled a K&N filter which made it restrictive but not noticeably by me whereas I put a gasket on upside down and that was noticeable. Perhaps as Willy has put you might have a partial blockage with most likely the gasket. You can get different, and differently made gaskets, some have two small holes some four, some the holes aren't fully aligned.

Physically profiling needles I'd have thought would require practiced skills.
Nigel Atkins

Chris,

I would suggest you need more static advance and less dynamic.

Normally the 123 is timed 'straight up', i.e. at TDC, with the distributor providing the both initial advance and the dynamic, hence the 10° static and 22° dynamic.

From the figures you quote, it looks like you are using one the 3rd group of programs (8 - B), which give 22° dynamic advance.

The total of 32° BTDC is the maximum for any scenario, make sure that you do not accidentally exceed this.

If you went to the 2nd group (4 -7 and 20° dynamic) AND set the static advance to 2° BTDC, that will give the same maximum advance, but more at lower engine speeds. Check for pinking at low revs, but I would be surprised if it is a problem.

If the 2nd group works, you could then try the same thing with the 1st group (1 -3 and 18° dynamic), but this time set the static advance to 4°. Obviously check for pinking.

You will probably find that more static advance will improve the idle and cold running, BUT without reducing the dynamic advance to match it, it is NOT a good idea!

Unleaded fuel needs more advance to fire well.

Richard
Richard Wale

This thread was discussed between 21/05/2020 and 22/05/2020

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.