I am not an expert, but I have a Street Avenger (670cfm) so that makes me one. Holley has a lot of video information which can help (HolleyTV). I agree with the others that the pump is one of the last things to tune. I set my mains by reading the plugs. Altitude effects jet size. I then set pump cam. Mine is the stock red. Never heard that you can't use brown cam with 30cc pump. I got the JEG's set of cams that has a useful chart of all the cams. I tried several more for fun than to cure a problem and found very little difference. They help some at this amount of throttle opening and hurt at another point, or RPM. Never heard that idle screws will tune anything other than idle and just off idle. Off throttle pop sound like too rich not too lean. As one of the Holley videos says "More isn't always better." The last thing I learned was to make one change at a time and to keep a record of what I did each time. Good luck and remember it's not a Weber.
Quote:
Originally Posted by genolan
I have a Backdraft 408 making 520Hp so the engine spec sheet says. The engine has vic jr heads and intake along with a holly 770 street avenger carb.
Other engine spec's are unknown. The car pulls and runs much better with the changes I made to eliminate the Bog.
I had some pretty severe bog and changed the squinter from .25 to .35 along with switching the cam from a green to brown. This took care of 95% of the bog with only hard acceleration from 2500 rpm giving a slight stumble(no black smoke at all when nailing it). Exhaust pipes inside look almost black.
Carb is stock with the following
pri jet 72
sec jet 75
pump nozzle increased from .25 to .35
pwr valve 65
secondary diap spring silver (vacumn secondary)
idle set to 1000 rpm
Issues?
Popping out of exhaust when at steady state 2500rpm and also when deceleration.
Should I increase squinter from .35 to .37 i'm trying not to go over this since i'm not comfortable changing the pump to 50cc.
I'm really enjoying playing with my new toy even though it's freezing out.
I haven't had a chance to check vacuum or timing yet.
Any ideas or is popping normal
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