Changed fuel filter runs like crap 1970 340-6

I changed my fuel filter today and now it runs like crap. Seems to be running on 6 or 7 cylinders and smells strongly of unburned and wasted fuel out the pipes. I also hear gurgling in the carbs after shutoff and see some steam come out the tops. Seems to be very rich, like it's drowning. It cranks and runs but barely with an extremely low hit and miss type idle.

I changed it because while it ran very well at low idle/fuel demand it seemed to run out of steam at higher rpms so I suspected that it wasn't getting enough fuel to meet demand.

I'm thinking the filter that was on it before was somewhat clogged or restricted fuel flow in some way and now that I've put the new one on it has opened it up and the engine is now getting more fuel than it can handle and burn efficiently. How do I fix this?

It sounds like a piece of debris from the old filter or lines found its way into the carb and is stuck between the needle and seat.If that's the case you will have to pull the float bowl.

Did you accidentally knock off a vacuum line or something? Do anything else to the car while working on this? Last summer I fixed a charging issue, started the car up and it ran like crap. Scratched my head and finally found I had taken the vac line to the brake booster off to get it out of my way...

Pull the plugs & see what they have to say

STOP!
based on the description of the problem it appears that fuel is leaking past the o ring on the needle/seat on one or more carbs.
You will probably see fuel coming out of the vent on the offending carb. Don't make this harder than it is

What needs to be done to fix? Only thing that's changed is the fuel filter.

As mentioned by others, you probably have some debris that you dislodged, could be small chunks of rubber, rust, crap, etc, etc,...you need to remove the needle seats from each carb and clean them, they are very delicate, they can be removed by removing the locking screw, then unscrewing them up and out of the bowl top, no need to remove the bowls, you'll need to reset your fuel levels after re-installing them, remove them, look for debris, some compressed air, and cleaner, make sure the needle seats actually move and seat in the assy

Mike

I agree, spray the assy with some brake kleen to clean it out & I would wet the O ring just barely with some oil on your fingertip so it dont catch/rip as you reinstall it

Do the carbs have to come off to do this?

No they don't have to come off, look at the picture above, this unit is right on top of the carbs.

Have a helper start the car, look down carbs to see which one is overflowing with fuel.

Remove that one needle and seat as Dayclona shows. Hold nut with wrench, loosen screw with a large screwdriver, then remove the screw and lift off the nut from the top and see how far down brass needle valve is screwed down so you can put it back in at least that far down or a little bit more so your float level is lower than it should be. Spray some luberication on the threads before removing the brass needle valve from the carb. Turn it with that nut, you may be able to turn it by Hand to remove it. Clean it out and reinstall.

Don't touch the other needle and seats yet.

Restart and look down the carbs again to make sure the oveflowing fuel has stopped happening. It is possible to happen in more than one carb, but one is enough to do this to your car.

Engine should run better now, raise RPM to 1500-1800 to help clean the plugs, depending if the plugs will clean up on their own without replacing or cleaning them.

Yep.... needle & seat on one carburetor OR you knocked off a plug wire or vacuum line by accident changing your fuel filter.

yep, a holley externally adjustable needle has more than one way to leak!
if they go into the bowls too easily, the o rings may have shrunk/hardened and will need to be replaced. Drove home in stop-and-go traffic one warm day, not fun!

I believe it's the front carb. I'll look at it tonight, but that's the one that was gurgling and both it and the middle one had steam coming out. Rear one was fine.

Wel that's it then. Do that front one and recheck it.

On any Holley carb. I work on to remove the needle and seats first remove the screw and nut without turning the nut. Once they are loose unscrew the screw and look at the position of the brass slot that the nut holds, now remove nut and needle and seat assembly together while counting the amount of turns (within 1/8 turn)it takes to get it out, write it down and then look very closely at the needle and the seat, there will be some debris in their, maybe really small If you can't see the debris and remove it either replace it with a new one of the same size or bigger opening that the needle seals on, they come in .090,.100,110, and .120 with the Viton tip seals on the needles.
When it comes time to reinstalled it or the new one use the same amount of turns it took to remove it as a starting point and go from their
BTW, Mopar six packs set ups rock Especially when set up correctly and jetted correctly for that motor
Good luck, let us know how you do and find out