It would be interesting to read the diff. opinions about various carbs, and why people like/hate them, as well as mpg info.

** Note, On Summit racing I read that the Holley 470 is not recommended for the street, but merely for off road use, and that it would run rich on the street. (Harte3, aren't you running that carb?)

 

I'm running a 4160/1848-1 465 cfm. Originally, Holley made them for stock replacement on smaller, older V8s...like the Holley 80555C is made as a QJ replacement and the Edelbrock an AFB replacement. I get 14.5+ mpg in town with cold starts and short trips and as much as 18.6 mpg on trips at 62-67 mph here in the PNW where there is no level ground to travel.

The best carb is one that is properly tuned, suits one's purpose and the engine "likes" it.

 

I feel sure this suggestion will give most a few laughs... Carter YF from a 1970 F350 [simple and reliable] with 16.5-18.0 mpg in urban driving and 22-23 mpg @ 55-60 MPH on a 1985 F150 with SROD transmission and 3.08 rear gears.

 

I certainly don't laugh at that...you make an excellent point.

 

Once you've decided to slap on a 4v manifold, I've always like Edelbrock carbs just because they will drive right out of the box and are so simple to tune. Half the changes - step-up springs and metering rods - can be done with the thing still on the intake. And the gasket sits on top of the fuel bowls where it's less prone to leak. No power valve to blow out (yeah, I know, they're blowout proof now...), no accelerator pump or vacuum secondary diaphragms to go north, freaking simple and reliable.

On my old F250 with a 302 (a terrible combination, btw) the mileage was better with the 4v intake and Edelbrock 600 than stock. With headers and a CD ignition too. I don't drive the Bronco as much as I should and haven't kept good track of mileage. Big 38 gallon tank but I never fill more than about half way and don't have to put gas in it all that often. I drive with a heavy foot too.

That said, I've got one of the small Autolite 4100 carbs that has the power valve and secondary/accelerator diaphragms I'm going to try. And my cousin's trying to get hold of a Predator carb for me. We'll see if they can knock an Edelbrock off.

It ran really well with the stock YF until it gave out around 3,500 rpm. That's a nice, simple piece too.

 

Still looking for that perfect carburetor.

I never did like the stock YF very much. I probably had to fix/rebuild mine about 3 times in the first few years I had my Bronco. Every time I'd go off-road, the metering rod arm would bend and ruin my adjustment. If it was too much, I couldn't drive home. All in all, I've probably spent more on my stock YF than I have on all the carbs and tuning I've done on my 4bbls since, including the intake. It also always bogged off-the-line.
Gas mileage was good though at 18-20 on the interstate and around 15 in town.
Once ethonol gas became the thing, though, it dropped to around 9 in town and 16 on the interstate.

The Holley 390 was nice, but gave terrible gas mileage (11 in town, 11 on the interstate), but I don't know if I just got a bad one. I did like the drivability of it.


The Holley 600 (which I'm trying right now) is great on gas mileage. I get a consistent 13 - 14mpg in town, and have been getting around 17.5 - 19mpg on the interstate at 65mph. The issue with it is the low venturi velocity at lower RPM that makes it weak/lean. From about 2000+ RPMs, it's a beast. I miss the crispness of the lower RPM acceleration of the 390cfm though.



How goes the Quadrajet venture? Any gas mileage returns yet?

 

The best carb is the one that works best for you and your setup.

I'm running a holly 390 with no issues and can get 15-16 on the highway if i baby it and tons of power to get over the passes here in oregon.

only thing I did was change the power valve to half of vacuum(8.5) as per tuning directions.

I dont really get into the power valve much in normal driving but when it's needed it does great... I have towed 6000+ pounds with no issues

 

How goes the Quadrajet venture? Any gas mileage returns yet?

AB--Remember I told you that I had used aluminum rivets to block the by-pass air passage? I took apart a Craig'slist qj and found oem plugs that looked very similar. I had to laugh.

I was removing the C.Ruggles restrictions in the air bleed, and when I replaced after testing I broke the airhorn. Now I'm back to the Eddy 500 and ten mpg, city or highway. (Yes, I know, but I have tried everything with the E. 500.)

I've been searching on ebay for a good core qj from a 301 or 305, and hopefully I'll be able to use my throttle plate base and not have to go through that again.

It was interesting to learn that C.Ruggles wants you to have .030 diff. between m. jets and m.rods. But research says the 301 qj's came with .072 jets and .052 m.rods. Very interesting.

 

I think all Q-jets are actually capable of the same ait flow. The only difference is in the secondary air valve calibration. So your base plate will probably work on most any Q-jet from the same era. The real early ones have some differences and of course the feedback Q-jets but I never messed with them much. Even if you have one calibrated for higher cfm, I would think you could just tighten up the secondary air butterfly to not open so fast. When you get into secondary metering rods there is a dumbfounding selection of different profiles and only an expert tuner will know the subtleties of them all. A good Q-jet tuners book might be a wise investment.

 

What I have learned after playing with the QJ's and reading about them for I don't know how long now (maybe 6-7-8-9 months?), is that most people believe one fits all. Yes, the s.air valve is one important aspect of calibrating a QJ, but there are untold differences from one qj to the next. Yes, GM did use the qj on everything from small v6's to 500 ci caddy engines, but the reason they were able to do that is not only b/c of the adj. s. air valve, but b/c at the factory different size restrictions were placed in fuel orifices. They also changed air bleed diameters, and the amount of air by pass, customizing each for a specific application.

Another thing I have learned is that once you change one of those orifices, you are out in no man's land, winging it w/o much documented knowledge to guide you. Cliff Ruggles' book is a good source for certain v8 formulas for changing said orifices, but, again, if you vary from his formula, you are pretty much searching in the dark, because each change you make is complicated by 4 or 5 more adjustments that can be made to mix, power spring tension, jets, m.rods, air flap, secondary hanger, acc.pump spring and length, not to mention playing with the v. controlled secondary lock out.

Unless you want to study earn a M.S. degree in QJ's, I say to set it up oem, and make minor adjustments from there. All important is finding a carb from a qj that GM installed on an engine as close as possible to what you are going to use it on. For example, if you're trying to calibrate a qj off a 350 for a ford 300, when all the orifices and airbleeds, etc. are designed by GM engineers to flow for a 350 v8, then you'll have your work cut out for ya.

And people wonder why the qj gets a bad rap! To compound the problem, it is my understanding that the untold reference books printed for GM, that told of all the carb details for the thousands of set ups possible for the qj, were destroyed when hard copies transitioned to digital. To the 'yo yo' at the Auto Zone counter, as to untold backyard mechanics, a QJ is a QJ. One size fits all. Yessiree bub.