Holley Avenger 770 extremely rich... Help!

[80Camaro]

I took this off of my engine about 2 months ago and rebuilt the engine because of a wiped cam lobe. The engine had been running perfectly before that happened. The only difference in the engine now is the slightly larger roller cam (From XE268H to XE276HR). I just started the car and it runs OK but it's extremely rich. It backfired out of the exhaust one time before I adj. the timing. I just checked the power valve in front and I don't think it's blown. Fuel level in bowl is OK. What the hell could have changed? It has the #72 prim. jets that came in it.

I am having trouble with timing. I can't retard it down to 34 total... not even close. Any thoughts? Thanks

[SpeedyV10]

I would try replacing the power valve since it did back fire (even though the street avengers are supposed to have million mile power valves). Are you running the correct number power valve based upon the amount of vacuum you are pulling?

Do you have a stuck float? Pull the bowls and check. Needle and seat stuck?

Did you balance the carb using the mixture screws?

Is it just running fat at idle, or does it stumble when you try to rev it up? Check the stroke on the squirter to make sure you dont have a lean or rich bog.

[80Camaro]

Floats are not stuck
screws are balanced
It's rich at idle and into the throttle... ALOT of dark smoke
I cannot see any fuel leaking into venturies with it idling and part throttle
I checked the power valve with a vacuum gun... it's not blown

[Nova-Mann]

I have a truck avenger on my 4x4, which has a 350 with a roller cam designed for high torque. I had (and still have) problems with mixture which I have never had with any other Holley. I could make it idle fine, but mid throttle acceleration was way rich. Cruising and full throttle weren't quite right either, and this was right out of the box. After what seemed like a million combinations, I gave up and put 3 sizes smaller primaries and 7 (yes seven) sizes smaller secondaries in. The secondaries are a little too lean, but I'm sick of messing with it. The signal from the cam profile really seems to screw it up. It seems to me that the power valve comes in at a really low #, something like 2.5. I'm looking at putting some sort of FI on. :mad:

Mine is a 670 cfm.