Idle drops during warmup/stall!

[65Valiant273]

1965 Valiant w/273 and 2bbl (stock)

Starts up nice and quick when the car is cold but within a minute or two of driving the idle speed will drop to around 400 rpm and threaten to stall or will stall completely! As long as I am moving the car drives fine and it will go away when it starts to reach operating temperature.. It started doing it intermittently a few weeks ago but now it does it every time I go out!

Do I just need to adjust the choke a bit? or is it more serious? (Cannot go get it tuned for another week or two..)

 

[AJ/FormS]

Could it be icing?
At temps near zero, and high humidity,like Vancouver at this time of year, ice will/can form at the leading edges of the butterflies, when they are opened just a little ways as in cruising. Then when you come to a stop the ice shuts the fuel off at the low speed discharge ports and the engine stalls.
The cure is heat. Heat under the carb and/or to the throttle plates. A heavy dose of Isopropyl alchohol in the gas can help. There is a passage in the factory intake manifold,under the carb. It connects the two heads together.Hot exhaust shuttles back and forth under there and heats up the carb to prevent icing.As the motor ages and begins to burn oil, this passage often plugs up with carbon and the heat is no longer sufficient to prevent the icing.Perhaps that has happened to yours.
About the choke. Yes if you can adjust it to stay on longer it may help.
Another trick is to heat the air before it enters the air filter house.Later model 318s(early 70s?) had a heated air system which you should be able to adapt to your carb.It consisted of a different filter house with a snorkel on it, a metal plate to bolt onto the exhaust manifold, a connecting heat stove pipe between the two, and a vacuum control system that made it automatic.It works very well, supplying air at/near 80*F . The carb was calibrated for it as well.

 

[krazykuda]

You need to adjust the choke so the idle is higher. be sure to adjust the screw for the FAST IDLE for the choke, not the warm idle on the throttle plates....

Keep bumping it up 1/8-1/4 turn until it stops stalling...

 

[Inertia]

This sound familiar,.. ??

Car starts well, you back out the driveway, come to first lite,, it's fine,, come to 2nd lite, it stumbles and dies,, instant restart,, come to 3 rd lite, it stumbles,, may/may not die,, and runs fine for the rest of the day.. Happens for 3 weeks to a month every year,, spring and fall..

It's icing,, if you adjust any screws,, remember where they were cuz it'll need to be set back in a few weeks..

To prove it,, At the same hour, take the top off the air cleaner, start engine,, and with flashlite,, look down the throat of the carb near the throttle plates, and watch frost/snow form around the inside of the carb base sufficient to plug the idle port, and transition slot,, closing off the flow of fuel.., when the snow melts,, the car will resume normal operation..

Things like stuck/no heat riser, plugged heat cross-over, contribute to this condition,, I tell folks to live with it the few weeks it happens, because the cost of repair can be expensive..

hope it helps