[Cliff R]

Below is some information I've exchanged with folks who are experts in their field when it comes to aftermarket carburetors and carburetor tuning (they do it for a living).

Before I retired I woudn't share this information because it looks like I'm trying to "bash" the competition to steer work in my direction. In any case, a couple of comments below from folks with EXTENSIVE experience with these things:

"The magazine and the tv hot rod shows do not want to feature anything that does not tell the tale they wish to promote. I have done some work with the new Edelbrock AVS2 carbs with the annular boosters that the media say is great but when I replace the primary boosters with a standard booster the car runs way stronger, so much for believing the media."


"I am backdating most of the newer holley idle wells to 0.106" since most newer holleys have an idle well that is formed with a tapered core plug and I always place the idle jet in the lower position. The people I knew at Holley had sent me a prototype of the 750 cfm ultra series carb that was built by Bo Laws and it was very nice but once they brought the production in house it was not as good as the Bo Laws unit. The idle jet is longer than the one Bo Laws used thus it either sticks out of the passage on the gasket side or out into the idle well which restricts the flow. I either shorten a new idle jet or install an allen head jet that I drill to size. These changes cure the lean off idle problems we see with most newer Holleys"

I shortened up the emails but I think anyone reading them can get the drift. Instead of correcting design flaws with their products these companies just continue to dump them on the market. At that point if the end user isn't happy with it he's either got to become a carburetor expert or hire one to end all the drama. Not a bad deal if you have a part-time gig on a picnic table in your back yard and know where to go in and make the needed changes to get that junk up to par. I started my business in similar fashion. I used to work on ALL types of carburetors until they got piled up too deep around here. Then I decided to pick one type and stick with it, which was a very good business decision. I still turn down at least a dozen jobs a week and I closed down that part of the business over a year ago!.........

[Jay S]

Interesting stuff. Seems like I recall the annular boosters on the AV2 loose about 50 cfm against the regular boosters like a AFB. At some point of performance you will notice that, but that will never show up on a stock 350. IRC, some guys pull the boosters on the AVS2 and put regular booster in them? The AVS2 is popular for the 68 to 71 Mopar’s that ran the original AVS. I have a tunnel ram combo I am working on I was thinking about using an original Carter AVS carb, probably not a AVS2.


Our experience has been you can take about any aftermarket 600 cfm carb to replace a 2 bbl and you will be blown away by the power increase and probably run just fine, improvement over and old used 2 bbl in pretty much every direction. It is only after a year or two and run some fuel thru the new carbs and all the poorly mfg’s parts inside the carb comes unraveled you realized what the expert carb guys where taking about.

But you do not always get that lucky. We have a nearly new Holley 750 Ultra that we bought cheap because it wouldn’t it run right on a friend’s 383 SBC 430HP engine. Speedway motors shop in Lincoln,NE worked on it, even had it on the dyno, eventually said it was “too big”. The guy just thru money at stuff and hires projects out. So he switched to a smaller Holley street avenger, it didn’t run right. Then he put a FI tech system on it. That didn’t work for him either. LOL…He ended up with a qjet on it! Another friend bought the basically new $800 Holley 750 ultra for $200. His q jet on his 455 was running terribly rich. So we helped him try the Holley. Basically new yet, it ran like total crap. Took it apart and had huge jets in it like it was an 850, jetted into the 80s.. Appeared the previous tuner was trying to mask a problem it had. We spend a good part of the day messing with the ultra and never could get it to run very well, seemed like it was missing 50 HP. Out of desperation we took the top off the qjet and Jet’s upgrade, the adjustment screw holding the primary metering rods had cam undone. Tightened that up, and pulled the ultra off and put the jet qjet back on, it felt like we gained 50 HP. Still have no idea what is wrong with the 750 Ultra. I was able to tune it so it at least runs well cruising. Full throttle though that new carb still has something very wrong.

[Tom Vaught]

Originally Posted by Jay S

Interesting stuff. Seems like I recall the annular boosters on the AV2 loose about 50 cfm against the regular boosters like a AFB.

Lots of bad info out there.

Each Annular Booster loses 5 cfm so a 20 cfm loss. PERIOD.

Tom V.

[Jay S]

Thanks Tom. There are only annular booster on the primaries, so at most 10 cfm, and they do not look very restrictive to me. I think the annular boosters were a pretty decent improvement.

On the fuel line routing you can move the inlet to the from the right side to to the left side on the carb and run a factory line for a 389 and an AFB. Not an exact fit but much better than routing the line to the back corner of the carb.