Hello everyone. First post and I may as well start with the current issue. So last fall I had the 68 out and punched it. Heard a loud backfire( don't recall if it was from the carb or exhaust). It suddenly stalled and didn't restart. Overall the car was hesitant. Wasn't moving the way it should. Timing was adjusted week prior and it seemed to move better. It's a 454, 750 double pumper holly ect. When I was getting my timing adjusted the guys mentioned I hardly had any vacuum. Would this possibly be a problem with starting? I was also told it might be the power valve that's blown. I'm unsure if this carb has a release valve and since it doesn't run I can't easily check if it's blown or not. I have not yet looked over the dizzy or plugs. Should I start there? Has anyone had this happen before? Not too mechanically inclined so I'm unsure where to begin. Any help is appreciated.

 

A blown power valve is possible if you have an old old Holley. But Holleys 1992 and newer have a spring/check ball safety to prevent a blown power valve during a backfire. That's not to say yours didn't blow for some reason though. To test the power valve, idle the engine, then crank the idle screws all the way in. If the engine kills, the power valve is not blown. If it keeps running, replace the valve. The power valves have different Hg vacuum ratings. You want one that is half of what your warm engine at idle manifold vacuum reading is.

 

Well as I mentioned the car won't even start now so I can't check if power valve is blown unless I take it out. Maybe that's where I should start

 

Good place to start - remove power valve, suck on it for test.

Reason for no start is probably spark plugs are dripping wet with fuel.
Remove, clean, dry, and replace.

 

The engine would still start with a blown power valve. A backfire, stalled engine, and no restart is likely to be an ignition problem. If you have a blown power valve, that would have been the result of the backfire, not the cause of it. I'd first start by removing the distributor cap, crank the engine over, and see if the rotor is turning. Something could have let loose with the distributor, or with the timing chain/gear. If distributor is spinning, put cap back on and check for spark with either a timing light, or by connecting a spark plug to one of the plug wires and touching to ground while cranking engine over. Let us know the results.

 

Great thank you guys for the reply. I have some household projects to do and still waiting for the weather to warm up here in Ontario. I'll update the post once I get it going.
I'll check what you guys recommend. Again thank you