Thanks for the updates. I have one question.
You mentioned using motorcycle jets as air bleeds. What size tap did you use for them? I have been using Holley air bleeds, available on line and even available undrilled, that use a 10-32 tap.

 

I believe it was a 5mm x.070 tap.
I have changed my metering rods out for 73 x52's also. The idea is to lean out the rich step slightly. Gas mileage has been a little less than ideal but 14.3 in a big tire truck is not horrible for the first "post tuning" tank in hill country, high winds, and 70+ mph speeds combined with dirt road travel I guess. I admit to still having fun "getting on it" too. This combo puts my old 400M (stock) to shame.
I wish I could get some 2" HG springs for the metering rod plungers. In 5th gear it is hard to stay above 3" of vacuum. I may do better using 5th only when going downhill to stay out of the rich step on the rods. I am only turning a little over 1700 rpm at 70 in 5th. Watching the multimeter on the dash I bet my mileage will improve noticeably if I do. In 4th at 70 I am still only turning less than 2400 rpm and barely feeding fuel from the transition circuit until I get into a steep grade. I really need to swap in 4.10:1 gears to be honest, then 5th would not be strictly a lugging situation.
I will update my results later. I am hooking on to a small camper and disappearing for a few weeks and will have averages for every type of driving when I return.

 

Very interesting results! It's nice finding someone else fiddling with a similar setup! My Edelbrock 500 AFB is an ongoing tuning saga right now as well. I actually need to lean the power step on the rod more while keeping the same cruise step, but they didn't supply anything I can work with in the tuning kit, so I'll have to order something or custom make something. Right now I'm on .083" primary jets and 6552 rods I believe. The 6755 rods were just too lean to drive well. But the secondary side is really where I'm having trouble getting a good AFR curve. I was thinking of installing adjustable bleeds on the secondary side, but right now I've just enlarged the high speed and low speed bleeds, blocked the early transition feed bleed, added and enlarged the emulsion tube holes and upped the jets an enormous amount. I'm at a .125" equivalent jet now to get 12:1 AFR above 2500rpm without having a 16+AFR transition below that. I've also added 3/8 holes filled with lead to the secondary air flap and about to try another to help with the under 2500rpm leanness. Anyway, I have a thread started on mine, but it's nice to see someone who knows a little about tuning these for these engines as well.

 

If you have the joys of cold winter weather, that will change things. I am retuning mine due to differences in winter fuel and the fact that cold air leans things out. Gufluh, I understand the custom rod thing. I have honed my rods down to 70x52 now. I can always buy unaltered rods for warm weather again.

My air bleeds are going to drop from .067 to .063 since my transition readings turned pretty lean once the temperature dropped. I was surprised how noticeable it was when the average daily temperature fell by 50 degrees in a few days.
Maybe I will screw with this stuff today since I am getting grubby with a partial front axle rebuild to replace old crap that time has just worn out.

Interestingly, I get 11.5 to 14 mpg empty no matter what I do. That includes a month spent at 2300' elevation and my running around at 4500'-6000' average where I live. Running hard or babying the truck and keeping an eye on the monitor. Towing a small camper trailer I knocked down 9 to 13.4 mpg. Hmmmm. I did get 16+ with the Autolite 4100 one tank full but it never ran nearly as strong and mostly returned 12 to 14 mpg. It looks like I need to build that set of annular boosters for the AFB...

 

I'm good on the cold weather front being in south La. And at sea level always, but I haven't had enough time yet to get a true mpg reading. Most of the driving so far has been at WOT and in town. I did just take a 200mi trip out of town for the weekend and it returned a measly 15mpg, but I wasn't trying for mpg and the first 5 miles or more were WOT tuning also. I averaged about 17mpg hwy with the Holley 600 and a max of almost 20 one tank I tried, but mostly 15mpg in normal driving. I did try for mpg on my way back this weekend, but I haven't filled up to check yet and unfortunately I left the laptop at home for the trip that is my only display for my wideband. It would have been a good time to watch and take notes of how it does on part throttle cruise at speed. I still have the stock 5" springs in it.

How did you "hone" the rods? All I could do is try to chuck the bent end in a press or hand drill and sand them down by hand while mic-ing.

 

I will say that my readings have all changed again now that I swapped the 35" tires for 33" tires. The small increase in rpm due effective gearing change has changed my vacuum levels as well. Now I can use overdrive without instantly going to rich mode at light cruise.

I used a small ultra fine diamond hone for knife sharpening and did the work by hand, carefully rolling the rod as I stroked the hone then lightly smoothed it up with 600 grit wet dry. Slow work for a few thousandths. This requires frequent measuring and a very skilled hand to keep things uniform and avoid tapering the step.

I was actually tempted to intentionally taper the rods, and even more difficult feat due to the need for perfectly matching tapers. The reason I didn't try it though was that I have no way of knowing whether the rods shift from lean to rich quickly or gradually around the preset vacuum rating of the metering rod springs. Anyone know?

 

I have had a suspicion that the rods do NOT snap up an down at exactly x" of vacuum. The way a spring works, it's rate increases and decreases linearly as it is compressed and decompressed. I just don't see the piston design allowing for it to snap up and down, as a valve would in say a transmission valvebody.

Also, looking at the rods I'm curious of exactly where on the rod it's running. Tapered rods would make more sense to me and have a slower transition from leaner cruise to richer power as vacuum drops. It would take some careful measuring, but I'd really like to know, because looking at the rod, it IS tapered on the lower power step and I don't see a reason for it to be, as it doesn't match the jet taper and it's length is way longer than needed to stick through the end of the jet with the lean step already out.

I'd also have to do more testing, but AFR seemed to correlate with vacuum on the primaries and richening smoothly as vacuum dropped and the throttle opened.

 

They definitely do not just snap open. The issue is that there is such a short range of travel from lean step to rich step that it may not modulate all that slowly and could be difficult to control.

The taper may serve the purpose of easing the transition from lean to rich rather than holding a specific flow rate between the extremes. Remember vacuum is also pulling fuel around the rod and a sudden drop in that vacuum due to sudden loss of resistance would cause many bogging and surging issues.

 

I thought about this while watching the monitor on my dash today. The rods do move from the lean to rich position (or vice versa) very quickly when it occurs. Even with steady throttle, as rpm drops ever so slightly around the preset vacuum point (thus resulting in reduced vacuum at a steady throttle opening) I read a rather quick change in air fuel ratio. It is most noticeable when in a tall gear for a given speed (as it should be).

This has me once again wondering if a long steady taper would be much better for the metering rods rather than a two step profile with a short taper between.

 

I noticed that some the last time I drove my truck. I was getting into the power step easily at lower rpm when the vacuum was low, but the power wasn't enough at higher vacuum to get going fast enough. Anyway, I have also been wondering why such the sharp transition step from cruise to power on the rods and why a more gradual taper isn't used. Looking at an EFI VE map and AFR, they definitely don't have a sharp transition, but a gradual one as vacuum drops/kpa rises.

 

It may be a lot easier (i.e., cheaper) to manufacture a stepped rod than a controlled taper one.

I have made tapered metering rods by taking a larger-than-needed rod and spinning it in a lathe to taper it down. A drill press or even a hand drill and a micrometer could probably work

 

I have been thinking along the same lines already!