Coming home from Carlisle my 440 + 6 pack
ran beautiful till i got off of 78 and stopped at a red light. It didn,t want to keep running and has a bad stumble. I guess it will be process of elimination till i find the problem. Run's nice and smooth at speed and pull's hard through the gears with the carb's kicked in. What would blow a power valve and how would the car run????

I would think a hesitation/dieing/stumble would be lean (vac leak) & this sounds like that as opposed to a blown PV which would put you on the other end of the spectrum which would be the power circuit would then be on full time & be too rich. (unless a blown PV stays "off") but that still would not make it hesitate/stumble at less than WOT throttle, it'd be like normal part throttle operation when you are on the "cruise" circuit.

Something else to consider is that if the fuel had been getting warm on the highway and when you came to a stop, it got hot which would show up as a lean condition at a stop.

Or, vacuum leak?

You've got a couple of possibilities for sure.
Extra fuel leaking in could be a failure such as
Accelerator pump check or power valve - in yoiur case could be due to somehting in th efuel damaging the materials.
or could be simple even loose bowl screws depending on the type of gasket (sticky type moer likely to stay sealed).

Or an overfilling bowl on decel is another possibility.

either due to float setting slightly high or needle sticking,
or related to hot vapor pushing fuel in.

Chrysler mentions that as early as this '63 MTSC
http://www.imperialclub.org/Repair/Lit/Master/188/Page13.htm

But it got more attention in the '70s
http://www.imperialclub.org/Repair/Lit/Master/271/Page13.htm

There's even a kit for it that I started a thread about a few years ago.


edit: How would the car run?
With excess fuel such as overfilled bowl it will flood and die nice and soft as you let off throttle.
or may cough and die at full stop.
with busted PV it may run ok but rich, requiring more pedal to get it to run well.

Check the float level cold and then go drive it and if it acts up remove the air cleaner and see if the gas is boiling into any of the carbs, if so that may be your problem.
BTW, how old was the gas in the tanks when it acted up?
Todays pump swill isn't very good in carbs, especially if it is more than a couple of weeks old in the summer

The pipes are grey to white in color , I use ethenal free gas. I started it last night since it is cooled off and same thing didn,t want to keep running so it isn,t heated gas. Hand throttled it when not running and looked in the center carb and it was getting gas.

Well depending on what you saw that may be the problem.
From idle to 2000 rpm or so, fuel goes from the bowl to underneath the throttle blades.
So if you saw fuel coming out the boosters or any other location above the blade - that's not right.

Just like shown in the illustration here:
http://www.imperialclub.org/Repair/Lit/Master/273/Page05.htm

Only slight difference from theory to implementation is many carbs have a portion of the transfer slot below the blade at running idle position.
Flip back through the pages for the float and bowl stuff.
Basically. the bowl is at close to atmospheric pressure and the under the throttle a vacuum is created. That's how the low speed (aka idle) system works.

The first thing I'd look for would be fuel dumping into one of the carbs at idle. Look down each carb while idling to see if there's excess fuel dumping into one of them.

When I had my 440 Six Pack, what you are describing was usually a leaking power valve. Ran in to it more than once.

Just started the car tonight and the gas fumes were so bad in the garage i had to shut it off. I believe after tonight it can,t be a lean condition.

hi

look at your hot idle compensator also , bad gasket maby ?

I'm sure a bad power valve would usually mean a very rich exhaust

There has been some very bad misinformation posted on here about having some of fhe transfer slot expose to make the carbs idle good, WRONG
The slots should not be exposed at all below the throttle plates, if they are your carb is not idling on the idle circuit only due to extra fuel being sucked into the motor from the transfer slots
I had to find out the hard way that opening the throttle plates enough to expose the transfer slots also allow the power valve circuit to start dumping extra fuel into the carb on low vacuum motors at idle speed with higher rated power valves in the carbs, motor had less than 6.0 vacuum at idle with a 6.5 power valve would load up and die until I increase the idle speed to make more vacuum than 6.5 inches of vacuum at idle speeds
Years ago someone, maybe Holley themselves, started drilling small holes in the throttle blades to allow extra air into the motor to avoid opening the throttle plates enough expose the transfer slots
Try removing the lead plugs blocking the outboard carbs. idle circuit mixture screws in the base plates and gently close them up and back them out 1/3 to 1/2 turn only and see if that helps on your problem
You can figure this out and fix it

I already had the fuel screws on the outers adjusted. It was running fine till Saturday when I drove it. So something happened on Saturday all I have to so is find the problem.

Today i started to check things out and so i started the car and it wouldn,t stay running till 2000 rpm,s so i shut it off pulled the fuel sight plugs and fuel trickled out all the carbs.Hand throttled it and the center carb was totally dry. i guess the next step is to pull the carb and see whats up. Any ideas???

Needle and seat is stuck more than likely.

Don’t even have to pull the carb for that.

I like to have the fuel level sitting at the bottom of the site plug hole, and not really running out.

I agree too. Just unscrew the needle/seat assembly from the top and blow them out with carb cleaner. You will probably find something stuck in one of them. Then screw them back in at about the same height that you found them.
Readjust like said above.

Could also be a blown/loose PV....... which would pretty much empty the bowl when the fuel supply stopped pumping.

Check the needle seat as stated in an earlier posting. I had the same thing happen last year . My 68 Coronet ran great at speed, but the moment I slowed to at a stop sign, the engine was stumbling.
This was right after I rebuilt the Holley carburetor. Took the carb off, took out the needle and seat, found the rubber in the needle and seat disintigrated. When I rebuilt the carb I did not replace the
needle and seat. Changed it out, reset the float level, installed the carb. Engine ran much better and no stumbling. Even when the car sits for about 8 hours; bump the starter, engine starts right up without
pumping the accelerator. The 318 runs great and idles great. The carb is Holley 500 cfm, 2bbl. It's the same as the Holley 350 cfm center board carb on the 6 pack engines. It's an easy carb to rebuild.

This.

It takes 20 seconds to do this and you'll know if it's a needle & seat. Get someone to help if it won't idle. Actually you can start the car from under the hood and hand throttle it and then you'll know.