For the last 6-8 years I have been wondering this same thing about Pony's and as of late a few of the other "carburetor specialist" who "advertise" making modifications to "improve" the 2100/4100.
I have actually had two of Pony's carbs apart (we won't go into that) which VOIDS their really good warantee, and have not seen any visual id of modifications performed. (which doesn't mean they have been done, I might add). I have talked to Jon (the owner of Pony's) and even one of his former employees, but both are mum as to what they actually do as for as modifications. (one because he cited propietary business procedures (Jon) and the other out of professional courtesy since Jon helped him get started in the carburetor business (and since he now also does a significant internent business advertising the (no doubt) same modifications).
I can tell you when I do a regular stock rebuild what I do that I would consider over and above your average rebuild, but there is no "trick" to it.
Firstly, and above all else, I make sure the carburetor is the correct carburetor for that intended application and it has the correct parts installed. Most all of the problems these professionals, claim to fix can be caused by having the incorrect carburetor installed. Change the carb to the correct application viola, problem gone. Same goes for when bench stting it or having the correct jetting and setting. If it is set wrong of has been "modified" by a "hot rodder" trying to get something more it can lead to common type problems, which can be esily corrected by simply bench setting them correctly. I see this in about 80% of the 2100/4100 (especially 4100's). A person who has documented this (such as myself or Pony's) can easily see that most problems are caused by incorect application and incorrect settings or tuning. I have seen 4100's with 10 jet sizes larger, I have seen 4100's with mechanical secondaries. Needless to say these were easy "fixes" to restore and correct the problems they came with.
Next, I make sure ALL PASSAGES especially the annular booster venturis are super super duper clean. These are OFTEN BLOCKED even in a just rebuilt carb. I test every annular booster I install, to make sure it will flow both air and fuel through its respective passages. I use a wire welding tip to clean and make sure the passages are clear, then use a special nozzle I have rigged up with the use of regular brake cleaner to make sure the passages flow, I then completely soak all of these parts in an ultrasonic cleaner to get them even more clean. The ultrasonic cleaner uses soundwaves to clean even the smallest passage of anything.
Most every carb I get that someone has tried to rebuild and still has problems with result from either one of these two above problems. Check this forum, same is true here!!!
I then go over every screw hole and retap them out with special machinist taps. Most people don't realize that taps come in two to three sizes for each different thread size and most homeowners taps are the H3 version which cuts the hole the most oversize possible per industry standards. Most machinist taps are of the H1 variatey and provide a chance to clean and dress the threads WITHOUT cutting them oversize. These are what I use. I also deburr the hole tops and then redress all screws or replace any that have the slightest burr or are stripped.
Next I use only quality parts for my kits, and because of that I use only motorcraft kits 99% of the time. Inferior kits lead to vacuum leaks and fuel leaks and even blocked passages.
Next I make sure all the original parts are in perfect condition and fit properly and I spend whatever time to make sure they do, or I replace those parts. I especially spend extra time with the throttle shafts and getting the butterflys to line up perfectly so they will operate smoothly. There is a difference between the primaries and secondaries of the 4100, install them wrong (and you can) and it won't work as well.
The choke area gets special attention from me since this is a high area of moving parts that often bind or will not funtion seamlessly. Many of the chokes are not working properly nor are set properly out there which then requires compensating someplace, which then messes up the balance of the carb.
I then use precision drill bits to measure all my settings, and all my bench settings are very accurate. As stated above my bech setting are correct for each unique carburetor, and only that particular carburetor. I use the stock jetting unless circumstances dictate a change (They most often don't). When I dail in a carburetor I use both a HIGHLY ACCURATE RPM GAUGE that reads fluctuations as small as 10 rpm (its digital) AND a VACUUM GAUGE. Without both you are just guessing.
The above represent what I feel is the highest level of work and one would be surprised that most shops will not do this type of quality.
As far as mods, the 2100/4100 can always have the venturi bowls cleaned up of all slag and casting material left over. I have done this for certain customers although it is not needed for the vast majority of the rebuilds.
Further mods can include individual tuning for the unique individual application, but when I do this it is usually combined with engine rebuild and dyno time, and involves gas anaylsis and testing. Far beyond the scope of most homeowners.
I have also played with the secondary springs for certain customers to fine tune the secondaries to the individual application. Same with accelerator pump timing.
I do make racing 2100 carbs for my racing partner, I basically do all the things that I mention above. The only things I do different for those carbs is put them on a diet with my milling machine and a die grinder. Our rules state that we can do anything to the outside so I remove lots of material from the outside, including the choke assembly. I have dyno'd and flow benched our carbs and found the best amount of material to remove from the choke plate housing (its not all off). I also anodize coat the outside of the carb for aesthetic purposes.
Our rules state we can not do anything to the interiors of the carbs so......... I really don't mess with that......too much. I do clean up the slag/extra casting material and very, very carefully blend it in since we cannot do anything to the interior.
I also do make sure fuel can flow sufficiently and nothing impedes it into the carburetor bowl. I also make sure nothing impedes the flow of air into the carb and through the venturis and boosters and through the butterflys.
We are using 1.23 2100's (since I can't find the 1.33's and the 1.23's are READILY available). We have spent LOTS AND LOTS of track test time getting the timing of the throttle opening and opening of the power valve to coordinate with my partners driving style and our track that he frequents. Part of this is playing with the amount of shot that the accelerator pump gives.
One IMPORTANT thing to note, he is running a FULL RACE 351 ENGINE THAT WE ARE RUNNING AT 7600 RPM MAX THROTTLE at one track and 8400 at ANOTHER, we are using a 1.23 carb designed for a 1968 ford truck with a 352/390.
SO the weight of his car is approximatley the same as the original application (68 truck) and the cubic inches are very close to the same requirements as the original 351 versus 352/390). Although we are admittedly flowing more than the stock 1.23 356 cfm, and we have changed the shape of the accelerator pump rod and are using a different power valve than stock, OUR JETTING IS JUST ONE SIZE LARGER THAN STOCK. Up until two years ago (when we installed a larger cam as we started running a bit larger track in addition to the one we always run) OUR JETTING WAS STOCK.
I have always been up front about the work I perform. I have to be a bit elusive about our 2100 racing carbs and some of the things I do to make my partner competitive. I owe him that since he is still racing and has to go through tech still and I am his partner. I can assure you it really more comes down to individual testing and lots of time spent in the rebuilding process rather than some super secret cheat. In fact for our carbs I prefer people spent time "looking" for that super secret cheat as they then overlook some of the meticulous and time consuming "cleaning".
Of course I am not "selling" 600.00 dollar carburetor rebuilds based on elusive "I can't tell you or I'd have to kill you" improvements, nor do I "sell" rebuilds on these already fine running carbs claiming to cure everything including the common cold.
There are other things that are pretty common "carburetor tricks" but as a rebuilder of mostly stock and street cars (most all my work is for the concourse and restoration crowd), I find that many of these "tricks" really don't add much for the 2100/4100 carbs and many, many of them detrack or can cause reliability issues later (such as slabbing and thinning throttle shafts and butterflys) and should never be done for the street or at the level I play at. (maybe if I was in NASCAR....... :o) racing for the big bucks)
SO Howard, Thats basically what I do.
How about the rest of you???? What hot secrets or myths do you do for these carbs?
Common you "cheaters" out there what do you have for us.........anybody want to fess up???
I know you are out there, I have a bunch of your carbs that have come off of cars with some of your homebrewed modifications. :o)
Tell us what you have done (or a friend has done, thats ok) and why you did what you did? And what made you do that mod, who told you about it in the first place.
I also know several professional rebuilders peruse this forum, anyone of you want to chime in....
Lets see if we can get a good string going on this one.......
Bill White
White Automotive
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HAVE A NICE DAY!!!!