Thread: Pop Back Through Carb

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Hi guys,
I am new to this board and it looks great and looks like alot of knowledge and experience here and diversity amongnest the many car makers.

Maybe you guys will have some ideas on a problem a friend of mine is having with his new built 350 in his 69 Camaro.
What's happening is when you quickly open up the throttle on the carb it's pops back through the carb with a nasty flame.
My thoughts so far have been timing too retard, checked timing have at 36 degrees total timing. Though I am not real sure of the timing tab this
Missed wired distributor spark plug wires, checked out ok.
Worn exhaust lobe on cam, checked out ok.
Sticking intake valve, checked out ok.
Did compression test and also checked out ok.
Vacuum at idle is 10 inches at 800 rpm, pretty steady considering it has a pretty stout cam, edelbrock performer rpm cam.
Rebuilt the carb to insure no problem, the engine does have a little bog when the throttle is opened quickly. Did have a holley 750 vacuum secondary, changed to a smaller carter 600 AFB and it doesn't pop as much.
Some things I am thinking about, engine seems like it could use more initial igntion timing but would have to take some timing out of distrubutor mechanical advance.
Carb problems? Not sure here because every carb that was put on the car did pop even though the holleys we tried seemed to be worse.

Any other ideas you guys might have as to what this problem might be would be appreciated.
Thanks,
Don

sounds like it could be a lean condtion try closing the choke butterfly alittle to cut off some air and see if it gets any better
If it helps then it's getting to much air or not enough fuel
Hope this helps

MM64

I would also check lash intake valve could be open if lash is too tight.

How new is this newly built engine?
When I started off with many new engines I commonly come across that problem on startup and on heavy throttle. I don't think there is anything too wrong with the engine. There may be some tuning issues with those carbs on the input. The cam you said is fairly hefty so expect some of that overlap. I think with the bog and the flame you should tune down the jet size. The thing with a Holley is that they use power valves which shoot fuel very quickly on high throttle. So that may be one of the reasons that they seemed worse. That's all for now, I may think of something later or someone else will. Good luck.