I have a 440 and it always ran fine , this weekend it started missing , it starts fine when cold , it started missing about have throttle / under load , it does not miss while idling , it has a Holley 800 D/P and a Mopar electronic distributor with the box on the firewall , it is now hard starting when warm / hot , cold it starts fine , I am thinking it might be a blown power valve as smoke comes out of the exhaust when it finally starts , it seems loaded up and takes a long time to finally startand has never done this before , I think it is carburetor related , it seems the more I drive it the worse it gets , any suggestions , thanks.

I'd start by seeing what the plugs look like

Good suggestion , will do , thanks.

With more thought yes the plugs may have gradually fouled but it sounds like this was a dramatic change. I think you are right on track to checkout the carb, basics, PV/float level/saturation & #1 needle/seat bad. Keep us updated

Will do , thanks again for your suggestions.

I will get new Autolite 85's , since I am removing them I might as well install new ones , are they still the spark plug of choice?

Run a jumper wire from battery positive to coil positive. This can help you rule out possible ignition wiring problems via ignition switch, bulkhead, bad ballast resistor, connectors etc, simply bypassing all of this.

As your car is electronic ignition verses coil only, I am uncertain as to where to run the jumper wire to, but you get the idea. Rules are different for MSD system, coil only and possibly Mopar electronic.

Insufficent voltage to ignition system can cause exactly the problem you are describing. Jumper wire test will take less than 5 minutes.

Seeing you might suspect the power valve, a simple test, the air/fuel idle mixture screws on the primary metering block (1 on each side)located/sandwiched between the front fuel bowl and the carbs main body, start by turning one screw/needle seat all the way in gently seating it, (count the number of turns so you can return it back to it position)if there's no stalling or change in idle, then do the last remaining screw, if it idles with both screws seated, the power valve is toast

Be aware some Holley's have a reverse Idle screw system, turning the screws outward actual closes the seat/passage, but generally such Holleys have a tag/decal on the metering block on each idle screw noting "reverse idle system"

Simple test, cost you nothing, and eliminates the possibility of having a blown power valve

Another good idea , will check the power valve that way , thanks for the
info.

No, they are offshore source junk now, buy NGK ... yes offshore to, but not low bidder junk.

Too bad most stuff is made overseas now.

The possibility can exist that if your carb is running on the transition circuit because idle adjustment screw is set too high to compensate for other problems(such as not enough initial timing, bad plug wire etc.) that even with both idle mixture screws completely seated or all the way out(in other words no effect) that your power valve is still ok, not necessarily bad.

Not to suggest that your power valve is not defective, as the cause of your problem.

Wonder what a vacuum gauge at idle might read. How does exhaust at idle smell. What do tailpipe extensions look like. Any significant drop in fuel mileage.

This just happened this weekend so I do not know if it's burning more fuel , but it is way harder to start when warm / hot , I do not notice a big change in exhaust ,m the rear bumper is pretty clean no black residue over it , it has the classic Mopar exhaust turn down tips , will get into it this week , I wanted some feedback from you guys so I can check all the suggestions out , thanks again as I have plenty of things to check.

if the plugs ain't fouled you might check out the ign systems

Have your battery load tested....sounds like your battery is getting weak.

The battery is fairly new , it cranks over fine and the AMP gauge is just a bit over to the plus / charging side so the charging system is not working hard to charge the battery , but if all else fails then I will check the battery , thanks for all the suggestions.

The hard starting when hot sounds like it is boiling the fuel over in the carb. when hot. Check the spark plugs for fuel fouling and if so fix the primary problem also Part throttle missing can be caused by several different things besides fouled spark plugs
Let us know what you find

I worked on the car yesterday , I had to change the valve cover gaskets anyway so I installed new spark plugs , the old ones were a bit crusty , two of them had heavy deposits on the ground electrode so I guess they were not getting a spark or a full spark , they were all dry not wet from fuel or oil , maybe from the gas? they did not have a lot of miles on them but were eight years old , anyway the car is back to normal , thanks again for your help on this , I probably should have checked them first but I did not think the cause was the spark plugs , thanks again for all your suggestions on this.