1968 toronado won't start, backfires through the carb

Hi, I have a 1968 oldsmobile toronado I am putting back together. Last time it ran was almost three years ago, and I recently just replaced gaskets and the like, normal stuff. One issue I had was I forgot to take pictures of the vacuum lines before I dismantled it, and so they are reassembled as best I could figure it out. I put in a battery and the engine turns over, but it won’t run. I came to the conclusion that it could be three different things:

1: a faulty vacuum advance, causing the timing to be off so the combustion happens before the spark.

2:I somehow hooked the vacuum lines up wrong.

3: Because it was parked three years ago with not a lot of gas, there is debris and water in the tank and I need to fill it and run some sea foam through it to get it to work.

The hoses are hooked as follows (please excuse the bad vernacular, I am new to this and don’t know what some of the parts are called) On the front left side of the carb is a port that is hooked to the middle port of a device on the front of the manifold. The other two ports on this device are blocked off. On the right side of the carb is a port that is hooked to the right valve cover. The vacuum advance is hooked into the manifold, right behind the carb.

Alright, sorry for the length guys. Any insight would be really helpful.

One last thing: Could there be an issue with the battery not having enough cranking amps to get this thing running?

what gaskets did you replace. did you remove distributor.not likely vacuum hoses routed wrong will cause this problem. check points and condenser

I replaced intake manifold gasket, valve cover gaskets, water outlet gasket, oil pan gasket. Left the head alone, I think it should be fine. I did not remove the distributor, but I had to move it to get the intake manifold off. is that a problem?

try moving it a little, first one way then another. hopefully spark plug wires aren’t mixed up. did you pull off distributor cap.

" 3: Because it was parked three years ago with not a lot of gas, there is debris and water in the tank and I need to fill it and run some sea foam through it to get it to work. "

It’s going to take a lot more than Sea-Foam…

Forget the vacuum lines for now.

Make sure you have good spark and that the spark is occurring at the right time. A simple test light hooked across the points will tell you this…

Do you have any idea how many miles are on this engine?? Maybe it needs more than gaskets…

78,000 miles, it ran perfectly when i parked it. Actually 78000, receipts and repair stubs verify this.

Backfiring through the carburetor is often a sign of the timing being advanced too much.
This can also be caused by contact points closing up, which can be common and happen pretty quickly on an aged car when a dry distributor cam lobe chews up the fiber block on the points.

could you explain what you mean when you say “contact points closing up”?

If you remove the distributor cap you will see 8 lobes on the distributor shaft underneath the rotor. The high point of each lobe is what rubs against the fiber block on the contact points and opens the points.
If the contact points fiber block is on the high point of one of the lobes and remain closed this is what is meant by “closing up”.

Bring one of the lobe high spots up on the fiber block and there should be a gap present (about .016 of an inch) or use a dwell meter to check the dwell (more accurate).

You did not state if you have a timing light and if not you can use this method to get the timing close (sort of).
Bring No. 1 cylinder to the top of the compression stroke (NOT exhaust stroke) and make sure the timing mark is aligned on zero.
Make sure the rotor is pointing at No. 1 on the dist. cap.
Rotate the distributor until the points just begin to open. Then nudge it a bit further. It should run on that anyway.

Another thing that could be causing this problem is a dirty carburetor. A clogged or sticking accelerator pump circuit in the carburetor can cause spitting back out the the top of the carb. With the air cleaner removed and the choke flap open, look down in the carb (engine not running) and operate the throttle by hand.
You should see a couple of streams of gasoline squirting from the accelerator pump discharge nozzles every time you open the throttle. If not, the carb needs to be overhauled.

Hope some of that helps.

It’s been a while since I have done anything with any carbureted vehicle, so I could be mistaken, but I don’t believe the vacuum advance should be hooked into the intake manifold. It should be hooked up to a ported vacuum port on the carb. You may be getting all your advance on startup, causing it to backfire through the carb. This is assuming you have the distributor installed correctly. Dropping a distributor can be very tricky for a novice and you could be off by a tooth on that helical gear. That would also cause your symptoms.