Factory Carter AFB CFM Ratings Chart/Rebuild pics.

 

  The question about this CFM chart by carter wich btw I also found on several other websites has this 1 1/4 primary venturi 575 carb.. none of the AMC AFB's had it. 

  My guess is that depending on the size of the engine the secondary valves may or may not fully  open and that is what is meant by the carter carbs flowing different CFM totals on certain motors? This is how the aftermarket AFB's were ultimately advertised-the secondary velocity valve allows only the amount of CFM that the engine demands-I remember the ads vividly. The 290's no doubt had a smaller AFB, my guess is though that the 390 and 343 had a 625 and that that is what they are capable of flowing if the engine will demand the airflow and pull the air valve all the way open.  Several of the larger carburator restoration company websites also explain that AFB muscle car carbs were not rated in terms of CFM.   That settles that I guess/  To do an accurate independed CFM test today youd need to know the exact method of testing and you coudl probalby get all kinds of different results for the same carb, and you would need to be able to measure the CFM and get an accurate number.  The manufactureres of the carbs already did that for the respective carb numbers.

 

  When the "aftermarket" AFBs came out the same size venturi and bore combos as the 343 and 390 carbs were 625 CFM on the competition series carbs.  A LOT of the new edelbrock parts interchange with the AMC OE AFBs , you can use an edelbrock performance tuning kit by using the flat step up rod cover and edelbrock jets and rods to replace the older AFB raised primary jets and 3 stage longer step up rods and raised cover. This gives you lots of jets and rods to choose from. The venturis interchange, the difference being the edelbrock carbs have a bottom feed booster and the carters have front feed. The secondary air valve and throttle plates too.  The accelerator pump parts also interchange except for the shooters wich on an older afb mate flat to the air horn casting. On the edelbrocks there is a round casting on the back of the shooter that would have to be ground flat to fit on an older AFB, the newer shooters have longer squirters that put the pimp shot closer to the venturi.  You can also use electric chokes from the new carbs to retrofit. The idle screws do not interchange, the newer edelbrock carbs have longer ones. Also the new edelbrock gaskets are slightly different for the main body, they cover the hole at the very front of the older AFB's.

 

  One thing about the older AFB that you need to look out for is the vacuum passage in the primary bore that leads to the choke housing. It will cause a vacuum leak if not being used.  I made a small gasket and placed it between the carb flange and choke housing so no vacuum can leak.  I am still going to install the choke housing cover and heater tube bracket for a stock appearance.  I am almost done with the rebuild, installed the annodized parts off the 750 such as the acc pump linkage and cover screws and secondary linkage.  I am going to richen the jetting over the stock jets. Should be a very torquey combo.

 

290 AFB's were in the 500 CFM rating category

 

343-390's used the 625 CFM rating equivalent carbs

 

Non of the AMC AFB's used 1 1/4 PBV so non of the AMC AFB's were 575CFM category carbs.  Interesting stuff finally some hard facts!

 

 

348 AMX,

 

I'm really glad that you started this thread,and that we finally got to the bottom of at least the cfm debate.

 

The earlier post that you put up on the AMC AFB carb specs., finally opened my eyes .That's a juicy bit of info. in itself. Where did you come up with it?

 

I will admit that I was leaning toward the carb being of the lower cfm (575),but I can now say with certainty that they were 625 cfm.

 

I tried to edit my previous post to make the first and fourth image as large as the second and third,with no luck.I hope that those pages are readable.

 

Rich C.