400 dies out when coming to idle
 

74 400 bored .030 over, 62 cast heads with the horrible eight relief pistons. Just rebuilt the 700 Holley double pumper at the begining of spring. Plugs are tan. has been running really well till last night. No bogs or hesitation, idled at 800 rpm's in gear. On the way home last night I had to two foot it to keep it running when not on the gas. Seems like it's loading up on me. at a red light the idle would drop from 800 to 600 and then start to stall unless I feathered the pedal to keep it running. Fuel pressure stayed a constant 6.75 lbs. Needle never moved till I shut it off. Sitting in park in my driveway it did the same thing. 6.75 lbs fuel pressure, idle 800 to 600 to stall. All within twenty seconds. pulled both float bowl sight screws, and fuel was just trickling out, both bowls full. Checked all vacumn fittings and lines/plugs. Still intact. Did not check spark , but does not instantly cut out like spark. Will fire up after stalling. Got gas about a half hour before this happened. Bad fuel????

Unleaded fuel? Why are the plugs tan?

I think I'd be looking for some trash in the float bowl. Maybe a small piece got in the needle and seat area?

If at idle and looking down into the primary's and you see no fuel dribblingout of the boosters then I would say that your fuel level is good and if you hook up a timing light and see it able to flash at idle then your spark is likley good also .

Next check your timing at idle.

After that I would pull all the plugs and check for even compression within 8% in all cylinders.

To check for bad fuel if you have rubber line feeding the Carb then run the motor a squeeze it off until the motor runs out of fuel, next get some known good fuel and pour it carefully ( I use a spray pain can cap) into each of the Carbs vent tubes until it shows in the sight plugs and then see how the motor runs for you.

Sounds a whole lot like a leaky power valve to me.

Border line, if not exact, text book on the symptoms.

Clay

I have seen a similar issue on a friend's engine when he did not have the throttle linkage quite right and the secondary blades were slightly open causing extra air to leak past the rear blades at idle. Lean condition and then stalling.

Tom V.

I did notice I could grab the throttle linkage and pull it forward a touch, and the rpm's would come down. It was not hitting the idle screw. I did readjust the throttle. It helped a lot, but a few times at a light I did get a lower idle where it wanted to stall till I feathered the pedal. It's inconsistant right now. I need to drive it some more to see how it acts.

If you can pull it forward to hit idle screw then either your return springs are weak, on the wrong angle to pull it home, or your cable isn't quite right to let the throttle relax onto the idle screw. Could be the throttle plates and shaft are binding for some reason.
You could start by unhooking the cable and springs, rotate the accelerator and see if the travel is easy and unimpeded.

I've had fuel boiling issues when running the car for a while

You answered your own question. If the throttle is not closing without help by pushing it closed, that's the problem. It's likely that the throttle sometimes does close completely and the engine dies.

I've found this problem sometimes happens only when the engine is hot. The throttle shaft or throttle arm on the carb may bind only when hot. A stiffer return spring rarely fixes the problem. Check the throttle cable carefully--ease of movement and adjustment--the most likely candidate for sticking.

Let us know what you find.