I thought I was done the project. The car runs good, starts right up, has power, good smooth idle.

I filled the tank a few days ago, put 54 miles on the car, filled back up, she took 6.96 gallons. You do that math, thats 7.7MPG. Now its cold in new jersey, but I'd like to think that I've got a MAJOR carb problem.

The Holley Street Avenger 670 is a goddamn EXPENSIVE carb, its brand new, and seemingly is treating me like crap. My buildup is not that radical. Do the secondaries run under part throttle and are not working? Are my primaries not working right? Do I need to change my vacuum advance curve.

The car doesn't smell rich at idle. My only idea is that the carb is dumping way too much fuel under load. I didn't do anything to the carb but set the idle mixture screws and set the floats. Both are perfect.

 

What kind of transmission and rearend gears are you using? What was your mileage before the build up?

 

Stealth: Please dont use that kind of language on the board.

It's obviously dumping way too much in under load. Gotta be under load since it doesn't smell rich at idle. I'm no carb expert so I can't really help you out. I was under the impression the Street Avenger was a bolt on and go? This is why I stay away from carbs Good luck to you. I've been keeping track of your progress and now finally she runs but sucks fuel eh?

-Corey

 

Don't believe the advertising. There is no such thing as a bolt on and go carb.

 

It sounds like it's dumping too much fuel under load. I'd re-adjust the idle mixture screws.

Maybe rap on the fuel bowl with a hammer too.

Look insode the carb while the car is idling. If the secondaries are dripping or anything...that's not cool.

Do you have a 4200 stall or something?

 

A friend put one of those Avenger 670's on his car ('66 Chevelle 327) a few years ago. Since then, he has been constantly messing with it to get close to the fuel economy he had with the worn-out Q Jet the Avenger replaced. The Avenger does come with a set of springs for the vacuum secondary side, where the stiffest spring supposedly gives a bit better mileage. Even so, his mileage is not too bad, just not quite as good as the Q Jet was.

In any case, did you use a vacuum gauge to set your idle fuel mixture screws? What is your initial and total timing? At what RPM does your full advance come in? Those few tuning items can make an enormous difference in fuel efficiency.

 

Well you might want to check for a blown Power Valve or incorrect Power Valve for the vacuum it's opening at. On a modified vehicle like yours, you usually must change them according to vacuum for when you want them to richen the mix.
I'd get a good Holley book, or consult who sold you the carb, or speed shop around there. Of course I'd check the easy stuff first like "Float level" and "Idle mixture"..

 

15" of vacuum @750RPM. More then enough for the power valve in there.

I've got 3.23 gears and the stock 700r4.

Right now I'm at about 10* initial, with 28* from the vacuum advance. Which gives me about 38* total timing, I was under the impression that 36-40* was a good area.


Do the idle mixture slits supply any fuel during part throttle? Do the secondaries open during part throttle?