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MG Midget and Sprite Technical - Another Q for P Burges? GY vs AN needles

I've just discovered that my 1275 '73 midget has GY needles in it. Standard is listed as AN needles.

I took the pots off my spare HS2's from my 1275 '66 Sprite (which has AN needles), and compared the springs to those in the Midget. Both look the same. I assume then that they are both using "blue" springs.

The engine on the Midget runs ok with no flat spots, and the plugs, -- now that I've balanced and set the mixture on the carbs -- are a nice healthy tan colour.

So my qustion is, what is the difference between AN and GY needles, when using blue springs?
Lawrence Slater

Have a look on the mintylamb su website.
http://www.mintylamb.co.uk/suneedle/

Select your jet size and then select the needles you wish to compare.

Dave
Dave Brown

Cheers Dave. Great link. :).

If I did that right then, there's almost no difference other than a small amount at the bottom of the needle.

Am I right?



Lawrence Slater

Hi Lawrence,
That is what I gleaned from the website, yes, virtually no difference. A tiny bit leaner at low throttle and possibly cruise.

Dave
Dave Brown

GY's were fitted as standard to the 1098cc perhaps a PO changed the carbs?
Bob Beaumont

Maybe we now know the missing little ingrediant as to why one engine pushes out alot of oil and the other dosnt


~¿*

Prop
Prop and the Blackhole Midget

Hi Dave. If virtually no difference, makes you wonder why BMC bothered to change the needle at all on the 1275.

Could be Bob. I don't know the history. Could be carbs from a 1098, although they do have the timing cover breather take offs. So I guess not. They actually look refurbished though, not 40 years old. Shiny new bits on them under the dirt. contrast to mine('66 1275), that look 48 years old and are pretty much all original.

Again, could be Prop. lol.

Anyway, if the answer is GY vs AN, = doesn't matter much if at all, then I'll leave them there and won't spend any money replacing them.

Cheers.
Lawrence Slater

I wouldn't say it's no difference. It's 1/2 thou on diameter, doesn't sound much until you think that the gap between needle and jet is only anout 4 thou all round. That means there's be about 6-7% less fuel delivered, which is roughly the difference in air:fuel ratio between 14:1 and 13:1. Although on the road it doesn't make a huge difference and the car may well run happily either way, this bit of the needle is on the part of the needle which delivers mixture under cruise or initial throttle opening so it's worth getting right if you are a manufacturer to optimise economy and/or throttle response. Hence BMC's fine tuning.

The B had a change in needle spec when the breather was plumbed into the carb. I suspect the Midget's may well have been reviewed then too, but haven't got my books with me to check.
Paul Walbran

"""The B had a change in needle spec when the breather was plumbed into the carb. I suspect the Midget's may well have been reviewed then too, but haven't got my books with me to check."""

They were ... but I dont recall the needle ref # off the top of my head

Prop
Prop and the Blackhole Midget

Cheers Paul.

Well if anyone wants to send me some AN needles buckshee, I'll happily fit them to my Midget. lol.
Lawrence Slater

I thought you'd like the economy of the slightly thicker GY anyway :-)
Paul Walbran

No Lawrence likes free or not spending money today.

eddie
Eddie Cairns

Too right Eddie. :).

Paul, I'll work out the average mpg over 1000 miles and see if the GY's appear to make a difference. Did about 90 miles today, and don't seem to be suffering a noticable performance hit so I'm not expecting to see any great saving on petrol.

But if the GY needle is leaner for economy, that didn't stop BMC from sticking it in the Austin 1300GT, which had bigger valves as was a pretty quick version of the A-series. That had the same spring (light blue) as the 1275 Spridget, and GY needles.



Lawrence Slater

But a different air filter, all these things can make a difference.
But then it could slo be a case of "OK let's see what we can confuse them with today" :-)
I'm sure that must have happened sometimes.

PS It would be interesting to see if the theoretical difference transalets to a practical one.
Paul Walbran

Well so far I haven't noticed any obvious difference when warm. Although I might have to keep the choke out a bit longer with the GY needdles. Took it out in the rain the other day, much lower air temp than of late, and when cold there might have been a bit of a flat spot.

I might swap the AN needles from my spare twins and see what occurs
Lawrence Slater

This thread was discussed between 22/08/2014 and 27/08/2014

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