It sounds like you don't have a manual yet.  This is a good excuse to buy one.  In addition to the carb section of the Mini manual there is a Haynes manual for Weber/SU/Stromberg carbs, a book entitled something like "SU Tuning Tips and Techniques", and "How to build and power tune SU carburetors".   

Someone has posted a PDF copy of the book "Tuning SU Carburetors".  The link below is to a 49 page PDF copy of the book.
https://tecb.eu/onewebmedia/Tuning_SU_Carbs.pdf
You can never have too many reference documents. 

Burlen is the current owner of SU.  The links below are for several tech documents they post online.
HS Carb Operation:  //sucarb.co.uk/technical-hs-type-carburetter-description-adjustments
HS Tuning general:  //sucarb.co.uk/technical-hs-type-carburetter-tuning-general
HS Tuning single carbs:  //sucarb.co.uk/technical-hs-type-carburetter-tuning-single
HS Tuning multiple carbs:  //sucarb.co.uk/technical-hs-type-carburetter-tuning-multi

Some HS carbs have a lifting pin on the side which is used to lift the carb piston a bit during tuning to determine when the mix is "right".  Use the pin or a thin screwdriver in the carb throat to lift the carb piston 1/32" to 1mm.  Hold the piston in that position.  While you do this, monitor the engine RPM and listen to how it sounds.  When the mix is right the RPM will go up slightly, then drop back down a bit.  If the mix is rich the engine RPM will go up and stay up.  If the mix is lean the engine RPM will drop and the engine may even stall.  (See page 27 and 29 of the PDF document linked above).

One more follow up on this post. When adjusting the fuel to air mixture, how do you know when  it's too rich or lean or  "that's as good as it gets?"

I'm glad you got the engine running the way you want. 

I don't remember the disconnected wire.  Perhaps you can start a new thread about that problem.

Glad you got it sorted.

Yaaaaay!

So I started from scratch and redid everything. Took a few tries but whatever I did worked. Runs better now than before I started working on it. I'm guessing I choked out the gremlin that was hiding in there. Thank you everyone for the help and advice. I still have the issue with the loose wire cutting the engine off but as long as I leave it unattached, it runs great. 

I think you need to do a compression check.
If you don't have a gauge you can rent one from any of the parts stores. Check all four of the compressions and post the numbers.

Remove the distributor cap and see if you have points or an electronic ignition.

Have you done anything else except change the jet and carb gaskets?

 
Trying to rev it up

That's why I replaced the plugs today because someone mentioned that the plugs may be too fould to fire correctly. When I can get it running like this, if I pull either of the right 2 plug wires off, it continues to run rough. I can here the wire arching to the plug so it is getting spark. If I pull either of the left 2 wires though, it dies. The wires run to the bottom front of the engine where it looks like the plug into a distributo . 

That almost sounds like it is misfiring. Can you do a video and try to rev it up?
Does it still have points and condenser or is it electronic ignition?

And just like that it's back to not wanting to start or surge for a couple seconds then die. 

https://youtu.be/6jyJ2vVOGyg

https://youtu.be/704YGhOGZE8
Replaced the fuel filter and spark plugs, couldn't keep it running. Put the old waxstat jet back in and it starts but idles rough and still a sluggish response. Probably need to work on the fuel mixture?

I need to count my carbs. I must have 100 SUs and a pile of Webers. Found three sets of 998/997 twin 1 1/4 SU complete with shields linkage and horns today. Steve (CTR) Some body must need some carbs.

Steve, you used to have to install the old type linkage but now they make a kit which includes the jet and a small bracket that attaches to the waxstat linkage, easy peasy.

There should be a brass ferrule/tube stuffed inside the plastic jet tube.  The brass will prevent the plastic tube from collapsing when the nut to the bottom of the float bowl is tightened.  

If you buy the kit to make the conversion from Waxstat to standard jet a new linkage part should have been provided.  It is highly unlikely that the new linkage part will put the new jet at exactly the same height as the old Waxstat.  Tweaking the mixture setting will be required.

It's been awhile since I looked at changing from wax-stat to non. Seems to me there is linkage change involved which would or could change calibration.  I don't think over tightening gland nut would stop fuel flow. If I could post pictures I'd drive you crazy. Steve (CTR)

I'll try spraying some carb cleaner through the jet to check the flow. I do have a fuel filter right next to the float chamber so I'll check that as well. 

To CooperTune, if I'm having this much trouble just replacing the jet, I am sure to pull the last of my hair out trying to install a a whole new carb.

That's good.

Do you have a fuel filter? If so remove it and blow through it to check for flow.

Jedduh01. As for over tightening the fuel line and collapsing the fuel hose. The fuel hose has a brass ferrule inside it so i don't think it is possible.

To Malsals  point.  there could be an issue with the new jet giving fuel flow. Pinched or clogged or blocked jet hose tube.

 You should remove the fuel from the fuel bowl.
   I would use brake cleaner or  Carb cleaner = and you can spray into the Jet = you should quickly and easily see that fuel come back into the bottom of the fuel bowl.

OR vice versa.  Spray into the bottom of the fuel bowl where the jet hose connects.. and you should have the fuel bubble back out of the jet ( this direction is harder to get good spraying application of sprays.

You're checking for an unobstructed fuel supply.

As with this =if you jsut replaced the jet by pulling out the old one = and sliding in the new one. the car should resume 'same' running characteristics. (jet height should be the same old to new)


I am not for certain on this = could you over tighten the jet tube nut on the bottom of the fuel bowl and Choke off the fuel hose?

I'm a little late coming in here, I have a classic mini that I have driven 175,000 miles. I began that journey with a well used 998 power unit. It came with a HS4 waxstat carb. When it started going rich I replaced the waxstat jet with a new one and continued. After well over 100,000 that unit over heated on a 20 degree day when the by pass hose failed. I currently run a 1360 Cooper S unit with a single HIF44. I also added a tach, water temp and oil pressure gauges. Did you say you have checked your firing order?

My current project is a 1400 with twin HIF 38s. If you want to go to the more modern HIF 38 I should have rebuilt as well as ready to rebuild ones. Steve (CTR)

Are you aware that you can modify the waxstat to be a rigid jet?  Carefully pry up the fingers holding the bottom of the waxstat in place, remove the thermal cartridge inside, replace with two or three pennies, and use pliers to crimp the jet back together.  You'll still have to make mixture adjustments.