Carter AVS metering rod adjustment?

[StockMan]

I have a carter AVS on a 1968 440, original pistons/intake/heads, MP magnum cam (dialed in to spec).  The carb is the smallar 625cfm unit (I do plan to upgrade at some point).  I have a bit of a stumble while driving at approx 2300-2600 RPMS.  Adjustments to timing has made a bit of a difference but I think the real problem is that I may be running a bit on the lean side at this RPM range.  The plugs read in at the lighter side of the healthy light brown.  I ran this same carb on a 383 I had in the car at one time and it always ran a bit rich.  That motor idled at around 13 units of vacuum.  The 440 I have in there now has way more vacuum, it reads in at steady 24 units at idle (which I'm told is higher than normal??).  I run an original distributor and have played with the dwell and find that 29 seems to respond the best.  Vacuum advance is currently not plugged in, it seems to be pulling the timing up to quickly, maybe due to the higher vacuum?  I'd like to address this to at a later point.

So my question is regarding the metering rods.  My understanding is that the engine vacuum is what controls their up/down movement, in term controlling fuel delivery.  Upper positioning allowing more fuel and lower allowing less.

So while the carb was on the 383, with less vacuum, the rods may have been positioned 'Higher' allowing more fuel, explaining my rich condition with the 383.  On the 440, can I assume that with the higher vacuum that the rods would be positioned lower, as compared to the lower vacuum 383, resulting in the leaner condition?

- Would it make sense to install slightly stronger springs so that the rods ride higher up that they do now?
- How does one setup metering rods so that they function at 'Optimal' position relative to engine demands for fuel?  This would seem to me like a very important area to have tuned properly.
- Or, do I simply need to install a different set of metering rods to get back to a richer condition?

Other that this I'm happy with the 440.
Thanks for your help.

[A383Wing]

while changing the metering rods are easier, it would be better if you just went up a couple jet sizes on the primary jets....finding metering rods a little smaller for 2500 rpm may prove difficult

Bryan

[StockMan]

Thanks for your response.  That does sound like an easy way to richen the mixture.

So could it be related to the higher vacuum in the 440 that may be causing the rods to be positioned lower, resulting in the lean condition?
Are there different springs that can be used to adjust the rod position relative to vacuum?  Or are all springs for the AVS the same?  It seems that this would be a very important area to be able to 'Tune' properly.

This article gets into some details regarding 'Tuning' the position of the rods in relation to engine vacuum, which is why I'm delving into this area.
http://www.diamondbackengines.com/technical-white-papers/carter-afbavs/

[Chryco Psycho]

you want the rods to stay down at idle in gear , if they do not then the spring is too heavy , when the vacumm drops at the throttle is opened they should pop up

[tan top]

you want the rods to stay down at idle in gear , if they do not then the spring is too heavy , when the vacumm drops at the throttle is opened they should pop up

yep     may be the elelbrock step up springs from a thunder AVS will work  in a OEM avs 

whats the vacuum reading idling  in gear ?

[StockMan]

I'll check the vacuum while idling in gear and report back.

[HeavyFuel]

Mopar Action has an extensive article on tuning Carters in the latest issue.  Check it out.

That sh*t was over my head.......

[StockMan]

Thanks for the tip, I'll have a look at that. 
I haven't checked my vacuum at idle yet, but I did take the metering rod springs out of the carb thats on the car, and also out of two other AVS parts carbs I have here.  I was suprised to see that all three sets are different.  The ones I had in the car are the longest ones, and they seem to have the most tension as well.