Sure, it looks about as right as any 'startable' setting looks. 

This is only where you get the car started and warmed up.  Once at normal operating temperature, you make adjustments to the mixture and eventually idle speed in an effort to get it running 'right'.  Sometimes the jet will be a bit lower, sometimes a bit higher - it all depends upon what the engine asks for.  My jet is typically just below the bridge - definately not 1½ - 2 turns down.  This is just what my engine wants for this carburetor type.

After you've twiddled the mixture setting into place and have adjusted the idle speed (if necessary), then you can remove the suction chamber and measure the depth of the jet from the bridge. 

Write it down - it'll be somewhat close should you for some reason or other decide to disturb the jet's position and need for a quick setting.  Of course, if you remove and replace the needle, it's all for naught and you repeat the process.  Another reason why I use a straight edge across the base of the piston when fitting a needle.  It's all about repeatability.

The jet holding tube is down 0.075" from the bridge and at 2 turns the top of the jet is down 0.165" from the bridge OR 0.090" down from the holding tube. I set it at a 1 1/2 turns which is 0.0675 down which is just a little over miniman's suggested 1/16".

Should the distance or number of turns of the jet be measured from the bridge? Maybe that's why it seems rich

Here's a picture with the jet 2 turns down from the jet tube. Does this look right?

[URL=//s129.photobucket.com/user/LarryLebel/media/DSCN1275_zpsze90fexc.jpg.html][/URL]

I've used the Minilamb program also, but I prefer Excel because I don't have to go to the website to use it and I find that the graphs I generate in Excel more easily represent 'lean' and 'rich' when thinking of fuel metering from the needle's thick to thin end.  Maybe because I'm right handed, but it works better for me.

Many years ago, I received the complete WinSu needle Excel files (fixed and biased for:  0.090", 0.100", 0.125") from Scott Bevis.  I've since added those needles which weren't in the original files by typing them in from Berlen Fuel System's needle profile chart booklet. 

Plus, I get to create cool graphs where I can simulate shaving a bit off of a needle here or there and seeing how it compares to the stock needle.

my favorite SU link

//www.mintylamb.co.uk/suneedle/

Man, I got that wrong...  In = richer, out = leaner...

Oh, well, here's a nice picture...

I used my old 2K rpm or less Color Tune to adjust the BDK mixture. Something must have gone wrong because the jet screw was all the way in. It started to run very poorly at low rpm and the plugs were sooty. Unfortunately its also burning some oil which is annoying because its a fresh +30 rebuild by the machine shop that did a fantastic job on the motor in my former Cooper S. The motor involved is pretty much a stock S motor which probably doesn't need a BDK which is why I changed to a BDL. The BDK needle was the one I had. Just trying to get the mixture in the ball park and go from there. Unfortunately, my patience and aptitude to do this s--t is not what it used to be.

When fitting a needle, I normally use a 6" scale held across the bottom of the piston which allows the shoulder of the needle and needle guide to butt against it.  It takes a bit of practice, but ensures that each needle is installed exactly the same.

That said, though, if you install your needle just a tad high in the piston, it'll remove the 0.099" dimension from the equation.  You wiill have effectively richened your idle mixture by repositioning the needle and not having needed to twiddle the screw too much.

I made an Excel graph of these 2 needles - very different, the BDK is much richer at full-throttle/thin end.  As you can see, they are very similar at slow-speed and light cruising.  I also added the BAK and BBC needles as mentioned HERE.

What problems were you having with the BDK?

I always start at 1/16 down from flush and tune from there, If you cant get it right from there then it's time to try a different needle

Wish I could vote up jeg's post as outstanding reference material.

Thanks jeg. I'm not sure I'm up to such DIY modification. I should have mentioned the mixture was probably way off originally with the BDK needle as well. I found on the interweb that a good starting point is 2 turns down from the the jet and holder being flush which I will give a try. The needle profiles you posted are imteresting. There appears to be a bulge in the BDK compared to the BDL at positions 3 and 4. I would have thought the profile of the BDK should be richer at every position.  

Image Gallery

Hi Larry, given that the idle mixture is governed by positions 1 through 2, I'd say you're right about it running poorly at idle.  It looks like you're probably 70% or more too lean.

Since the remainder of the BDL needle is within a useable leaner profile than the BDK needle that you replaced, I see two possibilities for you.

• Set the BDL needle around 0.0015" - 0.002" higher in the suction chamber piston thereby richening up the entire needle without changing its profile.
  • Drawback - difficult to duplicate the exact postion in the event that you need to remove and reinstall the needle at a later date.
  • Benefit - easy to do...
• Cut a very thin strip of emery paper, gently mount the needle's 'top-hat' collar (not the spring retention 'snap', but the larger, maximum diameter) in an electric drill chuck - taking care not to damage it - , center the needle such that it doesn't 'wobble' in the chuck at slow speed(may take several attempts) and gently reduce the needle's diameter between points 1 and 2.  Concentrate more on position 1 than 2, gently removing brass to 0.0965" (or as close as you can get without going below 0.0960", 0.0970" would be 'safer', but leave you with a needle that's a bit lean throughout - though you could probaly adjust the jet to compensate) without creating ridges.  If the tophat gets damaged by the chuck, gently re-profile it by using a file.
  
  • Drawback - the risk of removing too much brass.
  • Benefit - fit the needle flush in the suction chamber piston and forget about it - easy to remove and replace without messing up your calibration.

Looking at the '% change' graph for 0.100" jets, I find that if one moves from 990 to 964 (a 0.0026" change), which is a monstrous percentage change.

For those who haven't used these graphs before, I'll quote from the SU Needle Chart booklet:

"The graphs, one for each jet size, show the percentage change in jet area when adding to the diameter of a needle.  The horizontal axis gives a series of needle diameters and the curves rise in steps of 0.001".

The line of the lowest curve, for example, gives the percentage change in jet area at points along the length of any needle when adding 0.001" at that point - ie adding 0.001" to a needle diameter of 0.085" (in a 0.001" jet) brings about a change of jet area of 6.5% at that point.

The graphs plot the effect of adding to a needle diameter (ie going weaker) but they can also be used, with reasonable accuracy, when subtracting from a needle diameter (ie going richer).  The desired change in mixture strength is, of course, related to the change in operating jet area."

Hope this helped -

Assuming the proper needle, how far down from the the top of the jet holder should the top of the jet be, either an actual  measurement or the the number of turns down from flush. I changed from a BDK needle to a BDL and now the mixture is way off.