Mid Range Engine Performance Issue

[cannunz546]

Just so we all can understand. You replaced a new looking Edelbrock Thunder Series AVS with a truly new Edelbrock AVS2, and that fixed the problem. The AVS2 is the same carb as the Thunder Series AVS except for the booster venturis that are annular discharge like Ford 2100, 2150, and 4100s have used for about 55 yrs. The annular boosters do atomize the fuel droplets better. That's the reason Ford and recent Holleys like the 4180 use them. In Edelbrocks the boosters are modular parts that can be transplanted to other carbs so if Edelbrock would sell you (or anyone) a pair of AVS2 boosters you could easily install them in your Thunder Series AVS and it would become an AVS2. Edelbrock has done this before. The AFB and AVS off road carbs are simply the run of the mill carbs with spring loaded needle and seat assemblies. All that said the different booster venturis aren't likely the cause of the mid-range loss of power. If you disassemble both AVS carbs and compare the the jets, metering rods, and step up springs, you're more likely to find what the cause was.

That makes perfect sense JCKKYS. That old carburetor has given me problems every couple of years. It's probably because I drive that truck less than 500 miles a year and it's 15 years old since that engine was installed. I do treat the gas and store it inside, though. In terms of the replacement carburetor, I can tell you the engine now runs like new. It pulls like never before without any hesitation or stutter. I'm sure you are correct about the real issue. However, the new carburetor was $400 installed. I don't have the skills to diagnose and rebuild the old one and it was less expensive to replace it. The mechanic who helps me with this truck couldn't believe the difference in performance. I must say that your ability to diagnose the issue and your knowledge about these carburetors is super impressive. People like you are a dying breed. Thank you for your comments.

 

[cannunz546]

I run the same carb, except manual choke version. I ended up tuning mine with a wideband, ended up jetted way down.
Was running too rich. Keep an eye on your plugs.

Also, any reason you're running full manifold vacuum to your distributor?

That's the way it came from the engine builder 15 years ago.