Explain these AVS carbs to me--diff between '68 & '69.

[375instroke]

I saw these two carbs, both Carter AVS 4618S, which are for '69 440HP A/T non-air.  I thought the '68 carbs had one idle mixture screw, and '69 and later had 2.  Here's an example of a C9 4618S (March 1969 date code), with the two screws:



This one is coded November, 1968, and has one screw:



Here are the numbers on it:


Can anyone explain what's up with these carbs?  I need a 4618 for my car, and it was built on September 4, 1968.  Did they change something mid year?  Why wouldn't one have one screw, one have two screws, and they both have the same number?

[Dans 68]

My research on the subject reveals that while the '68's did have the single idle mixture screw, so did too the early 69's. So what you have are the two correct carbs for the '69 440 auto's. Based upon your build date use the single idle mixture screw carb. Good find, by the way...nice to have a date correct system!  

Dan

I attached an exploded view of the AVS carb, noting the comment about the early '69 single idle mixture screw. The cover of the reference is also attached (out of print, by the way but available used. Try Amazon).

[resq302]

If you look at the carb number for the one that has the two mixture adjustment screws, the carb number should end in SA.  The single higher mixture screw (which is a left thread) was an early design which did not provide adequate enough adjustment.  That carb number should end in S.  I think the change over was Jan. of 1969 or sometime close to then.  There was a topic on this in the Winged Warriors / National B body owners assoc news letter a couple years ago expaining this in detail.  Pretty much had to do with changing emissions requirements.

[chargergirl]

That was some amazing information. Learning new stuff here all the time.

[resq302]

You will occasionally see a carb number with the suffix SB.  The S was the standard factory spec.  The "A" was added to denote a factory revision to the original specs.  If you should be lucky enough to find a "B", that just means the factory made a second revision to the original specs.

[375instroke]

My manual only shows the single screw carb. with "limiter screws" where the two normal mixture screws would be with plugs over them.  Could the plugs be removed and the carb be converted to the two screw configuration with good results?

[resq302]

As far as modifying a carb, I really don't know what would our wouldn't work.  I would contact a carb rebuilder before you do anything.

[62 Max]

My manual only shows the single screw carb. with "limiter screws" where the two normal mixture screws would be with plugs over them.  Could the plugs be removed and the carb be converted to the two screw configuration with good results?

I think you will find pre adjusted mixture screws behind the plugs.

[375instroke]

I've got 91,000 miles on my motor, and find it hard to believe that the factory adjusted setting would be optimal for my car.  Are there only tiny screws that fit in there, do they require the plugs to prevent leaks of either fuel or air, can normal screws with the springs be used in their place, or can the plugs be removed, the screws removed for cleaning, be reinstalled and adjusted, and then left like that without plugs?