Please advise/suggest jet selection for a 272 with a 57 Ford 4100 carb. Carb has 54 primaries and 59 secondaries. 57 3 speed o/d Custom, performance cam.

Thank you all in advance for your help!!!

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The '57 carb came with .055 primaries and .048 secondary jets. The Hot Rod Ford Performance Manual from 1962 recommended upping the secondary's to .050. for the 312 engine. I would think that would be a good starting point.

Thank you very much. I am confused by the different specs for the jets. 57 ford manual has 54 listed for secondaries, 54, 52 and 50 based on altitude. Eaton carb test used 47 primaries.

Does anyone have a suggestion for the parameters for the 57 ford carb that will be ok with the air idle jets

My concerns are 1, what effect does modern gas ( 93 octane) have on jetting and 2nd, the carb was used on a motor with 40 more cubes.

Thank you all in advance! The car is all 57, intake, carb and. exhaust (312 duals). The cam has .485 lift, 238@ .50 (284 advertised) and 16 degrees of overlap.

Thank you all again!

4100 jetting. What jets are guys using in a 4100 ford carb on a y block?

smokey: with due respect to all, your engine will dictate what jets it wants. Ideally, a quality O2 sensor will tell you where you are at but all is not lost fi you don't have access to one. The time honored practice of "reading the plugs" still has a lot of merit, IMO, even in the digital age. A little research on the net will reveal many articles on what to look for. Some indicators have changed a bit because of the fuel we are forced to suffer with but, the plugs will tell you exactly what's going on in your specific engine. I usually start with the stock jets but, the motor will tell you fairly quickly what it wants. I don't believe that anyone can tell you definitively how you should jet your carb without actually examining first hand what is going on. Ballpark recommendations are just that. They get you in the neighborhood but not necessarily where you need to be. Part of the fun of our hobby is tinkering and this certainly falls in that realm. Also, many other factors will come into play as you delve into this. Ignition timing, float levels, power valves, etc., you get the idea.

I did say starting point. I had a Carter AFB off of a 312 Merc on my stock 292 back in 1963. Ran great without any jet changes. Trial and error is the way to do it unless you have access to some good diagnostic equipment.

The jetting varies on the 4100 carbs depending upon the original application and the size of the carb. The carb venturi size will be embossed on the left side of the primary fuel bowl (ie. 1.08, 1.12). The actual part number of the carb which will help to track down its original application will be on the left side of the left front ear that's used to bolt the carb to the intake. Those numbers can be stamped very lightly making them hard to read without some thorough cleaning.

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The rule of thumb on carb jetting is to first begin with the factory supplied jetting and then make adjustments from there. Similar looking carbs may have different jetting simply due to differences in the supplied air bleeds and depending upon the intended application.

Lorena, Texas (South of Waco)

Ted,

Thank you very much! The carb is ECZ 57 carb , all markings are difficult to read, however the accelerator pump has the long snout.

The carb came with 54 primaries and 59 secondaries. The 57 Ford manual lists 54 secondaries and 50, 52, 54 primaries based on altitude.

The carb in your test used 47 primaries on a 312, so I had some questions for a starting point for the 272. I am leaning towards buying a pair of

50's for the primaries and using the 54's in the secondaries. Of course going to lean is the big concern but we all know lean is mean.

Do you think it is ok to start at 47 in the primaries and 54 in the secondaries.

Finally, is changing only the primaries ok when testing or is it advisable to change both primaries and secondaries. We are mainly interested in

low end throttle response.

Thank you again, we realize this is trial and error and may end up re installing the stock 57 cam for driveability.

Without knowing the markings, I don't think anyone can give you a ballpark for the correct jetting. Try it as is and see what happens.


Lawrenceville, GA