i just put on a 570cfm holley street advenger on my 302 and its supposed to be ready out of the box...I get a back fire from the carb, it looks like its form the bowl vent. WHat could this be?

 

Double check your timing.

 

timming is set. i changed cabs yesterday and i didnt have this problem with the old carb

 

Your timing HAS to be off. Even if your carb was literally pouring gas through it and pooling, it will NEVER backfire through the carb unless your timing is off. Id also say recheckit, cant hurt. Also, Im wondering why such a small carb? A 650 is perfect for a 302.
-P.

 

i got out off the car and was testing the carb and if im easy with it its fine but if rev it pops from the choke side passenger side barrel. i can slowly inclease thje throttle and no pop but if i do it quick it will. do i have to let it warm up before i can rev even though the choke is open?

 

i had a 600 but it leaked, and this is the only other carb we have. holley recomended the 570 but i think its small also, its a 345hp crate 302 and it seems like its just killing the carb

 

I have doubts as to whether a 570cfm carb would be jetted properly from the factory. The 650 cfm would be a lot closer. You could be running very lean.

Take a look at the jets, you should be in the 70 size range. If not, get there. Also, the squirters will probably be a bit undersized and the accelerator pumps probably can't handle the volume needed for that engine.

Either you forgot to tell the tech at Holley that you have a 345hp 302 or he was a complete moron. True enough that a 570cfm carb should be able to get you 6000 rpm, but the circuits may not be able to deliver the fuel you need. A 650 DP would be a good cure...

 

i had a 570 street avenger and the jetting was way too small and i had to run the float bowles very high...i had no vacuum and had to change the power valve to a 3.5.

i changed to a 650 dp and it performs much better. i changed the stock 67 primary jets to 69. left in the stock power valve and have much better vacuum. my hp is about the same as yours, maybe a little less.

 

i'm not a carb expert in anyway so i would take the advice of those talking about your carb.

IMO, from my experiance, no matter how rich, lean or stoich you are running, you will only backfire if your timing is off. on my 200 cube i was off about 15-20* and shot a basketball sized flame thru my carb, singeing the hair off my arm from my knuckles to my shoulder.

i do agree that carb sounds a bit small for your motor tho.