Factory Carter AFB CFM Ratings Chart/Rebuild pics.

 

Q:  "May I ask a favor?" 

A :Yes

 

 

Q:  "In that book do they recommend blocking the hot idle air compensator valve?? This is the "winged" valve in between the secondary boosters."

A:   As far as I have read in the book,it does not recommend blocking off the hot idle compemsator. As a matter of fact ,unless I missed it somewhere,the book does not say a whole lot about the HIC.

In does show one in the rebuilding section and goes on to say that :"It allows additional air to bleed into the intake manifold during high-temperature operation"

 

I wanted to know more so here's the skinny:

During prolonged idling periods ,when it is hot outside,the ambient underhood temps can get hot enough to start to vaporize fuel,that is in the carb.. When this occurs,the fuel vapors get sucked into the engine ,causing a rich condition. The HIC is a thermostatically controlled device (bi metal element) ,that when heated sufficiently ,will open a passage enabling air to flow into the intake ,thru a passage below the secondary throttle blades,to even out the rich condition. When the air around it cools sufficiently,it closes off the air passage and then the carb. goes back to normal operation.

 

I think it a matter of application as to blocking it off or not. If said carb is going on a stock car,then make sure that it's sealing properly ,as to not cause any unnecessary lean condition, and let it do it's job.

 

If you are looking to use that carb for race application then removing it and blocking it off may have some advantage, in cfm if nothing else,as it does cause small restriction to air flow.

 

 

 

 

 Q: " As for the primaries there are 2 types of boosters; one without distribution tabs and one with, they are small aluminum strips installed at the bottom of the boosters to aid fuel distribution, does that book mention them at all?  Thanks!

 

A: Yes! Here's what the book says:"However ,any booster design is limited in its ability to distribute fuel evenly around the throttle bore.When poor (on specific original equiptment applications where poor) maniflod designs compound this fuel distribution problem ,Carter engineers frequently add a tab or mill off a portion of the trailing edge. These modifications "shape" the low pressure area such that exiting fuel is pulled into a more desirable distribution pattern"

 

 

Make sense?
Hope this helps. I know that I learned from it.

 

Rich C.

 

Main body completely cleaned and inspected.  I had initially dunked it in a bucket of carb/parts cleaner then rinsed it with carb cleaner spray. Blew it out with compressed air and then washed the whole thing in soapy water repeated with a carb spray can cleaner. 

 

This pic shows the venturi clusters installed with new gaskets and torqued down, it's important to clean the "wells" underneath these clusters that are supplied fuel from the bowls:

 

 

 

This pic shows the cleaned bowl cover, all passages were blown out with compressed air. Choke plate has been cleaned and it is staying there but will be blocked open as it directs air flow to the boosters.  Also note the flat metering rod cover that allows the use of edelbrock and 9000 series AFB rods and jets.

 

 

  This pic shows the annodized accelerator pump linkage and idle adjustment screw that I swapped over from the 750 Comp AFB, I also installed the Pump from the 750:

 

 

 

 

 

 AMC rated the carb @ 1.0 inch Hg, wich is a bit misleading, since at that rating the carb is flowing  "only" 430 CFM!  Carter rated the carbs at 1.5 and the same carb under Carters rating method nets 625 CFM. Facinating! Its a good illustration of how a CFM "rating" is totally subjective and can advertise the same carb as different sizes based on the parameters used.  A lot of the advertised CFM ratings for carbs today are based on tests that assume a greater pressure drop @ WOT than what was used by the companies in the 60's.   Double pumpers have a greater pressure drop @ WOT than Vacuum secondaries carbs since you can open up all the barrels instantly at any RPM and thus cause a greater pressure drop than is possible than with a vacuum secondary carb for the same given RPM, this also creates a denser mixture and more power when the carb is tuned right.   THe advertised numbers for holleys today would be less if they used the method for CFM common in the late 60's. But bragging to you'r local cruise night pals that you 3310-2 flows 780 CFM sounds a lot better than 575, and it makes for great marketing.   If your engine can create the pressure drop at wot advertised for a given carb than that is what it will flow, if the pressure drop your engine creates is less then the tested drop for the carb you are using the carb will flow LESS than the advertised CFM.  This is why the same carb could flow different CFM'S on different engines @ WOT.