A 3-Ohm coil is sufficient, and usually the perfect choice. Lower Ohm coils sconsume more current (Broadly, Current equals Voltage divided by Resistance) which points and more common mini electronic ignition modules are not designed to supply. They will burn out unless you have something designed for the role. Accuspark sell a module that does cope with higher current, if you need one.

The last T in GT40T responds to the shape of the coil as a resin filled "Transformer" coil shape, nothing else. They are 3-Ohm coils.

The Bosch SU12 and GT40 are the reasonably common coils on the shelf of the local auto stores. Either of these will do. Avoid the SU12R or the GT40R which will be beside them on the shelf. These are the lower Ohm coils we speak of.

The R in these last coils stand for Resistor. Some models of Minis (particularly overseas models) used a resistor mounted on the coil for voltage supply during normal running. When starting the voltage went directly to the low-ohm coil instead of through the resistor providing a stronger spark when the battery was loaded down with the starting current. This helped make cold morning starts easier, but was only used for a few seconds each drive so didn't cause a problem with the points, apart from added complexity.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

GT40T is the replacement for the (oil filled) GT40. It is potted in epoxy, as are most modern coils these days. Both coils are 3 ohm.
Electronic ignitions for Minis generally need a 3 ohm coil, many will fail with a 1.5 ohm coil as the primary current doubles.
GT40R and GT40RT ane 1.5 ohm coils.

Do not confuse this with electronic ignition used on modern cars, many use coils of 0.8 ohms or less because they are designed for it.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Ok so a new GT40T coil has been fitted however it appears was not the issue. No harm done I guess always good to replace these things from time to time.
However I have been looking into some of the other ideas brought up and 1018cc suggested that while driving and the car starts to struggle pull out the choke and see if it improves. Well it did. With the choke out the car ran better and didn't struggle as the revs went up.
What I need to determine now is if it's just an adjustment thing (keep in mind the colour tune shows a good reading as it is current set at) or its a fuel delivery issue.
Feel free to give your opinion

Again, I would probably look at your needles. At least take them out and see what needles they are.

They're unknown at this time. They tune up at idle, but that is not how it works. They rely on the taper being correct to carry that same tune through the rest of the engine load range.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Thanks, I understand. I took then needle out of one so far and it reads code- ABC

I think I need AAU or AAA. Suggestions? Looking at the stats for the ABC is doesn't get as rich as the AAU as it goes up in the increments which could be the problem

It will be hard to tell just from looking at graphs of each needle and taking into consideration that everyone commenting on this hasn't been for a ride in the car to know how bad it is but.... I'm looking at the comparison between an ABC which runs with the choke on and AAU and AAA and there is ALOT more fuel added in those two. Maybe you need it, I haven't been for a ride in your car but if the needle is too rich there is nothing you can do about it. If it is slightly lean you can richen it up a little by sanding it down. Depends on how many $$$ you want to throw towards needles - you will get there in the end (also, I am biased as I'm a tightarse).

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"In two years time your car will be like a lady's clothes, out of date, my car will still be in fashion when I am dead" - Sir Alec speaking to Pininfarina

It's moments like these you need a portable a/f ratio meter, so you can go for a drive and test under varying loads & rpm.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Does no one in the ACT have one or want to go for a drive? I've lent mine out to a member on here to tune his needles - they are really worth the money.

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"In two years time your car will be like a lady's clothes, out of date, my car will still be in fashion when I am dead" - Sir Alec speaking to Pininfarina

I would, but I'm working away from home!

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Hi Bazz

I perserved with a similar problem many years ago with twin SU's. My motor is an 1100 in a slightly higher rate of tune. I got hold of a SU tuning book which lists all the needle profiles.

I tried all the needles that gtogreen1969 suggested. The best result came from an EB needle with GG in the mix as well. Both needles are weaker than the standard recommendations.

Going by the specs, AAU and AAA will be far too rich for your motor.

Thanks for your post. It is dificult to make reconmendations via the internet I know, without seeing the car. I appreicate your advice on AAA etc being too rich however both the EB and GG run leaner than my current ABC so I may be going the wrong way. I checked this out at www.mintylamb.co.uk which shows the comparison of the needles.

I think I need a major improvement in the amount of fuel I am getting not just a suttble change. lol

A small update and a few more details.
As suggested I checked for air leaks in the manifold and surrounding connections and luckily ( mind you the only luck I had as you will find if you read on) the system is leak free.
I found something interesting that may help narrow my issue down and perhaps lead away from a needle and carby issue back to a electrical issue.
Please keep in mind that the car is currently in the "finishing restoration" phase and not a everyday car with a few minor bugs. I say this as I have discovered today that there alternator is not charging the battrey and to go one step further the alternator is not even putting out any charge what so ever. During my tune and the very short test runs the car has been running from the battrey. Yes the battrey has gone flat on a few occasions but I aways put that down to only having the car idle or because I was playing with the electrics and headlights etc.
So questions now go all they way back to the connection between my problem and the coil.
If the coil is not getting the full 12 v (GT40T) would this effect the spark? I can hear everyone typing yes already however I will continue. So understanding that the car is struggling to drive the thought was the coil was not producing enough spark to keep up. So I am guessing, and I am sure someone can confirm, that if the coil is not getting the 12 volts which would be the case as the battrey slowly drains would it create the sensation of the car wanting to die as the revs increased under load?
In my head this makes sense however it would not explain why when the car starts to struggle the pulling out of the choke would make it improve or when I adjust the carby to over rich the car run better. Maybe I still have a needle problem but I am sure that running the coil from a slowing draining battrey with no incoming charge has to have some impact on the drive.
Thoughts? Comments, told you so's?

As your battery goes flat and voltage drops, then eventually you will lose spark, yes.

A full battery without charge can run the car just fine for a few hours.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Once the battrey volts drop below 12 then there would be a problem for the coil?