To add to what Malsal says about checking the idle screw stop, make sure the throttle cable isn't too tight - I like to leave a tiny bit of slack once I get the idle set, in case I need to drop idle a bit more.

It sounds like you have covered the basics as i would have done. I agree take off the carb and see if the butterfly is lined up correctly.
As you have fitted the old carb and the idle changed the problem must be in the new carb.
When you look at the throttle linkage (the throttle stop/pad where it contacts the idle adjustment screw) in particular does it look to be in the correct position ? Where the idle screw makes contact the lever (contact stop/pad should roughly be horizontal on the same plane with the carb body where the idle screw fits if the shaft and butterfly are correctly installed. Hope this makes sense.

I imagine today's autoshop doesn't resemble the autoshop of our youth, especially when it comes to tuning. Back then, about the only electronic devices available would be a timing light, a dwell/tach and maybe a multi-meter. Nowadays, diagnosis is done by plugging a computer into the car's computer. 

Dan and Malcolm,

   Thank you for taking the time out of your day for a thoughtful response.  Before reaching these conclusions and levels of frustration, I did perform some of these additional diagnostic tasks.  As not many like to read a gigantic, multiple page post, I thought brevity would be my best bet.  Judging by a troll on this post, I thought wrong.  

  Prior to this post I had performed a propane vacuum leak detection test around different parts of the carburetor in addition to around the inlet manifold at the cylinder head.  With the amount of circulating air in the engine bay, however, I decided to repeat the test with starting fluid as it both ignites the hair on my arms quicker while also (usually) finding its way into open orifices quicker.  This time, however, it did not.  All new intake related gaskets were used (intake manifold to head, carb, air cleaner-to-carb, etc.).  In addition, I have welded in a bung into the new header at the collector and have hooked up a wide-band 02 sensor.  Readouts from this tool have indicated a proper mixture at idle.  

   Carburetor piston is the swinging needle type and drops down as you described.  Additionally, I checked dashpot oil levels and they are to spec (in addition to being the proper type).  Fast idle screw is backed off, as is the idle screw.  Completely.  Your methods of advancing timing to near pinging and backing off slightly to desired idle is the method I used with my Austin Healey (as taught to me by a race-winning MG guru from Wisconsin I met years back).  As this is my first Mini, I will definitely set it to TDC and make a notch on the timing cover.  I never thought of that, thank you. What I have not re-checked, however, is the centering of the butterfly valve on the newly replaced throttle shaft.  I will check that if time permits this weekend and report back.  Again, thank you.

Paul,

   Unfortunately, you did come off rude.  With your myopic post's only original thought being assumptions about my knowledge and skill level, its no surprise your remaining regurgitations were parroted bits of information from other members.  I can only hope your other 1000+ posts were not only more insightful, but also more polite towards other members.  Buzz off.

Not wishing to be rude but you say you teach auto shop? Yet you seem to be lacking in the basic knowledge of the how to diagnose a simple problem? Follow the airleak advise above and you'll find it. To set timing the pointer and marks are under the small cover plate on the clutch cover a mirror is required to get in there with a timing light.

Like Dan said probably a massive air leak. Spray some carb cleaner or starting fluid around the intake gaskets the revs should rise when you find the leak. If you don't like the idea of using combustible spray around the engine use a 3 foot piece of 1/4" hose and with it up to your ear listen around the gaskets for air leaks (hissing noise). As you went through the carb also check the piston is dropping fully down especially if you have a fixed needle jet and not the swinging one, with the damper removed after lifting the piston up it should make a nice clunk when it drops down if not it is sticking. This is usually caused by the (fixed) needle not being centered correctly, if you have the swinging needle there is no need to center the jet.
Lastly as you replaced the throttle shaft make sure the butterfly is centered so it closes fully with the idle adjustment and the choke fast idle adjustment backed off fully.

If you needed to set the mixture considerably richer, you probably have a massive air leak somewhere. The excessive idle speed also suggests that.

Start by checking the car linkage to make sure the screw that adjusts the fast idle is turned back so it does not interfere with the fast-idle cam of the choke mechanism. Then check to see that the throttle plate can actually close freely. It may bind if not centred in the throat. Not likely with a new carb, but not impossible. Next, check that the needle and main jet are properly centred - something that needs to be done on the fixed-needle type carbs. The dashpot should drop all the way down with a small clunk.

The next place to check is that the aluminum inlet manifold is sealed properly to the head. One common problem is that the flanges of the LCB and intake are often not the same thickness and do not bolt up properly. It doesn't take much. The solution is to machine them equal or use stepped washers.

When it comes to setting the timing, you have a problem not having a pointer scale. But you can figure out where top-dead-centre is by checking the marks on the flywheel. You will find them inside under a small plate on the top of the "wok"- the clutch cover.  The TDC mark will have the number '1' on one side of it and the number '4' on the other. From that, you can make a pointer for your pulley notch.

RPMs should speed up as you get closer to the proper timing, then should fall off as you go too far. You can set timing by ear (though it is risky) by getting the highest idle speed, then advancing until the engine starts to knock or ping, then turn it back closer to the highest idle speed. Then test-drive o ensure the engine does not knock under load. Remember also that initial timing should be set with the vacuum advance disconnected and capped at the carb. You should not have to retard timing to set idle.

Greetings everyone,

   I have a 1974 Mini 850 that I'm trying to get straightened out.  This past winter, I put a stage one kit on it and went through a couple of things.  I put the needle in the carb that came with the kit, aluminum intake, LCB header, and RC40 exhaust on it.  I bought a brand new HS4 carb off of ebay (went through it) and could NOT get the car to idle under 2800.  Putting my old carb back in with the needle, I can NOT get an idle below 1100.  I can't even shift into gear with the idle that high.

  So, here are my questions.  Could this be a timing issue?  I was going to time it, and there are no timing marks except a notch on the crank.  No gauge on the timing cover or anything. Starting the car, I can loosen the distributor (25D) one way, and get the idle exactly where I want, but  I have the boggiest throttle response.  I can turn the distributor the other way, and it will idle high but give me the throttle response I am looking for.

   What the hell do I do?!?!  I have new plugs in it, points are adjusted, wires are new.  I also replaced the throttle shaft in the carburetor as I found out the old one had worn out.  Everything else now is perfect.  No vacuum leaks that I can find, etc.  

I figured with all that air going in, I had to richen it up.  I did that (and the needle was changed, of course).  Any ideas?  With full time work and a baby on the way, I can only get in the garage about once a week but would appreciate any ideas you can offer.  I'd hate to have to take it to a shop (as I am a car guy. . . I even teach High School Auto Shop...I'm just baffled at this.  I never had this much trouble tuning my dual HS2 carb sprite)

Should I turn the distributor counterclockwise to (what I assume to be) retard the timing and then adjust the carb mixture to achieve the desired throttle response?  Is there a way to dynamically adjust and check the timing of the engine?  

Is there anyone I could bribe to come over and help in the Northern Suburbs of Chicago to come over and help for some beer and fine cigars?  Anything to keep it from going to a shop and taking an ego blow.  

THANKS IN ADVANCE!

Mark