carb issue? stumbles at stoplights.

73 Duster, mild '70 340. I've run a ThermoQuad on it that DemonSizzler originally set up for my failed 408 stroker. I've had no problems with idle or anything until recently. Car runs and drive great except when i pull up to a light...foot off the gas it idles but seems to cut out or drop out every 5 seconds or so....kinda makes the whole car hesitate for a second and makes you think "if it keeps doing this, it'll die"

It hasn't yet but somethings making me think the carb is loading up or something.

I thought about leaning it in some with the screws and at one point decided to run them in completely...I noticed this did NOT kill the motor..that made me think it's the carb as well.

Timing checked out good at 8 degrees advance and it's solid too. the motor has under 1,000 miles since the rebuild.

Any ideas on this?

T-Q's are good for a bad needle/seat inlet occasionally.

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Any ideas on this?

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take out the idle mixture screws and shoot a 2 second blast of starting fluid into each hole with the thin red straw then reinstall them where they originally were. But as said with them screwed in all the way it must be getting fed from somewhere; float prob/needle seat. Look down the throat with it idling then pull the air horn off & see what's up