Before I hooked up the AFR gauge, I changed the idle feed restrictions, the air bleeds, to smaller, from .046 to .043, and lo and behold, the mpg dropped a tad.

It is certainly time to install the AFR gauge and go by the book.

 

I have been seriously considering one of these for the 390 in the 74, so I'm eagerly awaiting your real world test and tune results.

On the other hand, the 300 in the 80 may be coming out soon. I have a hankering for a 5.9L 12V Cummins diesel, and the rattling 300 is making it even more prominent......

 

I hope to install the bung and gauge tomorrow, 10-15-13. I can't tell you how nice it will be to have the gauge guiding me. It is much needed and much missed in the past.

The top end is unbelievable with this carb. Now, if I can squeeze a few more mpg out of it for dd, I will be very happy.

 

We are all enjoying reading of your most recent carburetor experiences and along the way, you have acquired the reputation of being tempted to try multiple variants, so what about this?

http://www.ebay.com/itm/Rebuilt-Vintage-1970-Kendig-VVC-racing-carburetor-with-a-1250-CFM-/221293143823?pt=Motors_Car_Truck_Parts_Accessories&hash=item338619670f#ht_587wt_1170
Are you ready?

 

Ha, I've got a Predator carb - pretty much a Kendig knockoff - that I'll be trying here soon. I've got to finish fabbing a bell crank for the throttle before I can mount/run it.

 

Lol. Wow, look at that thing. It looks like the box that 'Thing' came out of on The Adams Family. That is a bit too wild for my blood.

 

Got ya!

 

Oh, they're pretty massive alright. Here's a Predator carb next to a 4100:

 

Great photo. 'Shoe box' meet 'hat box.'

Today I welded in the bung, further from the engine than I would like, but it seemed to work fine.

Idle, with .043 idle restrictions, I got 10.4--10.8. That was alarming. I switched to the oem .046 restrictions, and the idle reading dropped to 10.0 at idle.

I tested the cruise reading at 2,000 rpm I got 12.0--12.6

Since the larger restrictions made it richer I went to .041 ones, and the reading got better, 11.9--12.4 at idle.

I need a bit of advice here. Should I continue to drop in restriction size until I get to about 14.5--14.7? If so, would it be logical to assume that since I dropped 5/1,000 in restriction sizes, and the ratio went from circa 10 to 12, then I could drop 5/1000's more and the ratio 'should' go up from 12 to 14 to one?

With the cruise reading of 12.0--12.6, is that addressed by dropping a jet size on the primaries?

 

WOW. Well, the good news is that you are running rich. Those numbers would explain some gas mileage issues.

I believe idle you want a tad richer than cruise. Like 13.5 or so, but I can't remember. What AFR do you get at idle if you tune for highest vacuum?
Cruise.... stoich is for all around drivability and gas mileage. If you want a more aggressive cruise, closer to 14. For a leaner cruise, for gas mileage and such, you can get up to 16 or so. Sometimes, if you can get away with it without a lean bog, you can go 16.5 - 17.0.
You want your power circuits to be around 12.5 - 13.5.
Anything less than that in most any fuel circuit and you're just wasting gas and hurting performance.

Cruise AFR is most likely going to be with a jet change on the primaries, unless you fall into that irritating spot I did with one of my Holley 600s where my cruise fell right between the idle circuit and the primaries. That was irritating. I addressed that by putting a small piece of wire in the idle feed restrictions to bring the transition from idle to cruise at a lower RPM. I think you can do that with the air bleeds and such.

Sounds like you've got some great room for improvement!

 

Wow, I am very happy to actually be able to make adjustments/changes, and see instantaneously how it affects AFR. I should have done it years ago.

I pulled some numbers off the forum to guide me: 14.5--14.7 idle, 13.5--14+ cruise, and 12.5 + or - for WOT. But I'm always willing to learn if anyone has another opinion with the ratios. Just the change I made from circa 10 to 12:1 at idle made a difference in the pedal response.

Quite a difference with the idle restrictions. I've dropped 5/1000's and still need, I believe, 5/1000's more. (I found that Summit has the drill your own type for $2.90 for a pair.) I also have smaller primary jets coming.

I really love the efi mannies with the bung right there on each! Yes, the wheels/gears are turning ....

I may have to go back and retry the QJ, and see why everyone raved about getting 15, 16, 17, 18, 19 mpg with v8's and the QJ, and I was never able to pull more than 10 mpg.

But anyway, I'll stick with this carb for now, and hopefully get it dialed in when the parts arrive. And AB, good luck with your new carb too. Hopefully, we'll both be getting around 15 mpg city! kevin.

I got a link from another forum, and reading it makes me think I'm over my head. I know the link info is for a holley, but even so I don't want get so complicated, just tune and go. Tech | Burton Machine http://www.burtonmachine.com/documentationtechnical/

 

Where'd you read 13.5 - 14+ for cruise? That's a pretty rich cruise. 14.7 minimum at least, and even higher for some gas mileage.

I'll be very curious to hear what happens with your tuning and how the numbers change!
I need to get one on mine.

 

According to my handy Edelbrock carb manual...A/F ~13 at idle, 13 leaning to 14 above 3,000 rpm during part throttle acceleration, 13-14.5 leaning out to 2,000 rpm at cruise and leaning further to ~15.2 at 5,000 rpm. Twelve to 12.5 at WOT. There's a nice graph too.

Dunno that I'd go quite so lean at cruise without EGR, but then again I'm more than happy to give back a little mpg to ensure there's no pinging at part throttle. I might think differently if the truck was a dd.

Another question is whether a vehicle gets better fuel economy with leaner mixture and less vacuum advance or a richer mixture and more spark advance?

 

Yikes!! Someone tried to pass me getting on the freeway and I took it personally, and got on it. As soon as I got off freeway it almost died, chugging and running badly. Pulling over, I popped the a/cleaner and could see the primaries were flooded, and the secondary fuel level was at top of window. I keep the level at half window as recommended. I tapped and tinkered, revved with hand, and the level dropped to normal, then went back to top of bowl on the primaries.

I find this alarming because in the online review ( Summit Carb Review and Road Test - Ford Muscle Forums : Ford Muscle Cars Tech Forum ) of this carb, the guy's carb kept flooding and he had to get it replaced. Hopefully this is not a common symptom of this carb. I'm off to the garage to open it up and have a look. 'Just when it was running sooo nicely.'

 

I'm curious, how old is this Edelbrock manual? From what I've heard, newer fuels don't require things to be as rich as before. I've heard of carb'd vehicles running 17:1 to really eek out the mileage with no detriment to the engine. This, of course, is purely at cruise, in the flats, when your engine is just piddling along.

Ouch! That doesn't sound like a good trait.
My guess would be a weak needle/seat. When the engine's at higher RPMs, the fuel pump is pumping much faster, and the needle/seat can't keep the fuel back. Just a guess though. Hopefully an easy fix.
I remember reading that in the Summit Carb road test when I was toying with the idea of getting one myself. Fortunately, they should get you taken care of if it's under warranty.
I'd go out and try it again to see if it repeats itself.