Hi,

I live in the UK and am seeking some advice.

I recently acquired an Autolite 4100 off ebay here in the UK. It's part number is C5AF H, which I think is from an auto 390. I have read very good things about these carbs and I am keen to try it on my 351Cleveland which is fitted to an Australian Ford Falcon. The car at present has a 600cfm VS Holley. I also picked up a remanufactured square bore Autolite 4300 (which is what these engines came from from the factory).

(a) Regarding the 4100, can someone point me in the direction of a supplier of rebuild kits who would ship to the UK and take PayPal or credit card for payment ?

Also, everything seems to be present on the carb and all linkages work fine. The choke is present and operates as is should in closing and, sort of, setting the fast idle.

The main questions I have are regarding the throttle levers and the associated accelerator pump.

(b) Does the spring wrapped around the throttle shaft at the linkage hold the primary throttle plates fully closed, or does it rely upon an external spring to fully close them ? The wound spring pulls the plates almost fully closed, but there is then some free play which seems to imply another spring fully pulls them onto the idle stop.

Also, when the throttle is manually pushed to be fully closed, the lever arm for the acclerator pump does not contact the pump plunger. The throttle plates have to move a certain distance before the lever arm contacts the plunger.

(c) This seems to imply that there can be a bit of throttle opening before the accelerator pump shoots a squirt of fuel. Is this correct for a 4100 ? Most carbs I have worked with, and looking at the 4300 it is true, operate the accelerator pump as soon as the throttle shaft starts to turn ?

Being a bit on my own here, and never having seen a 4100 on another car, I have no idea what is right or wrong, so any and all help appreciated.

Thanks in adavance for any help.

Sandy Mercer

HAY Sandy,
Probably the first thing that should be done is to go to the PonyCarbs website. It's a marvelous place for those interested in the Autolite/Motorcraft 4100.

http://www.ponycarburetors.com/

Also:

http://www.carburetor.ca/

HTH

JC

OK, First of all good find. That C5AE-H is from a 1965 galaxie with the 352/390 engine, and is a 600 CFM carb.

Now which is the best carb Autolite 4100, versus Autolite/motorcraft 4300, versus Holley 4150/4160?

First the Holley,
Although considered the ultimate performance carburetor, and since they have been around since the late 50's, and now have several copies (barry grant, demon), the Holley is very tempermental.
Most used holleys that have been "found" have been "found" for a reason. There are many kits, doo-dads and options that are available for the holley, that most amateurs and "tuners" niether understand or realize how they effect the equilibrium of the carburetor. I often have to spend lots of extra time base-lining or re-setting these carbs back to the original setting. Many, many of these "found" have been modified so much that often they can never be put back to original settings. Of course the vast majority of these modifications are totally impractical for the streets and for street engines. In fact most of the Holleys themselves ( and their copies especially) are simply not street carburetor at all but full out racing carb. Holley 4150/4160's came in cfms from 390 all the way to 1150's. Many had mechanical secondaries. As you can see most all of these applications would not be practical NOR REALIABLE for the street or a street engine.
The other problem with the Holleys is they are notorious for fuel bowl leaking (which is a huge design flaw), metering blocks that don't seal properly or have fuel or vacuum leaks, and a mulitude of many small passages which readily clog and effect the balance and equilibrium of the carburetor flow. It has multiple pieces which makes sealing both for fuel and vaccum very difficult. The relaiblility of the Holley as compared to the 4100 is really questionable at best.
Finally because of all the adjustments possible and the differing settings it is very hard to precisley set a holley unless you have very sophisticated equipment beyong the reach of most backyard mechanics.

The 4300 is basically a ROCHESTER QUADRAJET in MOTORCRAFT desguise. In fact rochester designed the 4300 for FORD. The 4300 was design as an emmission carburetor and a bean counter dream, a few carburetors for many applications. This let to many, many problems with off balance issues for the differing applications. This carb suffered from off-idle flat spots poor, idle transitions and idle issues. It also suffered from choke issues. Again, a multiple piece carburetor, and one that had poor quality issues as well, leaking was a huge issue for many of these carbs. They suffered from warping and mismatch parts as well just to make things even more interesting. Several inherent design flaws some that are shared with its sister carb the quadrajet and several which are uniquely 4300 problems gave this carb a horrendous reputation right from the factory. To make matters worse the carb either came in an anemic 450 CFM or a gas bogging 735 CFM. Because of the so few models, choosing for applications is a nightmare. I rarely work on these because I consider them an inferior carburetor. And I never recommend one of these unless you are doing a concourse restoration and it just happens to have to use one.

The 4100 however is probably the very best street carburetor ever made (I know my opinion :o) ).
But this is the best realable carb built, the one piece base combined with the fuel bowls virtually eliminate leaking, in fact you can even run this carb without the top on, try doing that with any other carb. The 4100 only has a few adjustments and it is very simple to adjust this carb even with simple basic tuning tools (you all have an RPM gauge and a vacuum gauge right). Very few moving parts and in fact few parts at all. Ease to rebuild and work on using simple tools. A well designed carburetor with very minor inherent problems and even those are easily fixed. Many differing applications means even when adapting to something not original, the adaptee has a very good chance to get a carb that will work right the first time. Very reliable vacuum secondaries and the use of annular boosters provide even more realible service and performance thru-out the complete rpm range yet very dependable idle, idle transition, cruise and full rpm operation. Availability in both 480 CFM and 600 CFM makes it the perfect choice for both small block and big block applications.

Now to your specific questions:

The spring is not intended to keep the throttles close, that is the job of the external return spring or in some cases the throttle linkage has an intergrated spring. The spring that you are talking about on the primary shaft is the spring for the accelerator pump to throttle position relationship and to provide a return to neutral.
ANd you are right the throttle is intended to allow some opening before the accelerator pump adds addition fuel, ideally your transfer slots should be open to the airstream before any pump shot is added. this help create a venturi action and allows the addition fuel to atomize properly. When this does not happen or your pump shot is too great, that is the primary reason when you get that off idle bog.

As for your application that 351C needs and appreciates LOTS of air flow to keep those big runners supplied with fuel, normally 351 cubic inches still falls well within small blcok range however the cleveland is pure big block when it comes to air flow. So no problem with 600 CFM here, the biggest thing I see is your vehicle choice. The galaxie is a HUGE car, especially compared to yours. If I was choosing I would try to find a fairlane carb, but the real only choice you are going to have is the 66 fairlane 390 carburetor, a pretty unique, scarce and yep pricey piece these days.
That being said, I think you will be ok with that galaxie carb. You might want to adjust that pump shot by reducing it a bit to prevent any bogs coming out of the idle. Also depending upon which heads you are using, you will be wanting to make sure that big cleveland has plenty of fuel on the top end and not run it lean, so you might want to go ONE jet larger on the primary side. But odds are you will be fine just going one hole lower on the pump shot.

As far as the kit, What you want is a MOTORCRAFT CT-191A from any FORD DEALERSHIP, you can buy them also from many places online as well. This kit will have everything but the vacuum secondary diagphram which is available on E-bay or also from online sources (MOTORCRAFT no longer makes it unfortunately). Just google search CT-191A or Motorcraft parts

Good Luck

Bill White
White Automotive

Hi Bill,

Thanks very much for your reply.

I have bought a CT kit and fuel flter through ebay. Just a bit stumped on where to get the secondary diaphram, but I will keep a look out for it. I see some of the non-Motorcraft kits come with it. You would have thought someone sells them separately.

Thanks for the advice on the carb's suitability. I have read the forum closely and appreciate the views that the 4100's were very engine specific.

The Cleveland I have is a 351C rather than an 302C (which was a short stroke 351C and Australian only) so it has open chamber heads, it is also a 2V port size rather than 4V.

The Australians used 4300's in all the four barrel Clevelands, including the GT's. The Phase cars and RPO83's used 730cfm Holley's, but they came with factory headers anyway. I bought the remanufactured 4300 just as an exercise to remind me of how it looked. As my 351C is out of a much later Australian engine, they used Carter Thermoquad's which, at 750cfm, seem a bit over-rated for a 170hp engine.

I am not a Holley fan. The Falcon has a 600cfm vac sec on its 315C at the moment. I have not run the car enough to see if it is okay. I also have a 1969 Ford Fairlane Cobra with a 428CJ and it has a 750cfm vac sec Holley on it, but, despite a rebuild, I have had nothing but trouble with it. It was rich before the build and it is even richer now (at idle) and I just can't get it sorted. Having said that the engine is tired and the carb may not be getting a satisfactory vacuum signal.

Before the Fords, I used to run Buick 455's and got very good at working on Quadrajets. They had little idiosyncracies, but once you knew whta they were, I could get it to work very well. Good on economy as well.

I am hoping for good economy out of the 4100. We can't really hope for anything else considering gas is about $10 a gallon here.

Thanks once again. No doubt there will be more questions. I hope you are feeling better.

Sandy Mercer
www.aus-ford-uk.co.uk