New carb and intake and weird idle

[Phil21502]

on my 74 dart sport with a 318/904 I just swapped the factory 2 barrel for an edelbrock performer intake and and a edelbrock 650 avs 2 carb. Car starts and drives great. Only issue is when idling for a few minutes once its warmed up the idle will drop about 300 rpm for about 15 seconds and then go back to normal setting for a few minutes and then it drops 300 rpm for 15 seconds and repeat this process. Lol. Does it in park and drive. Also once warm if you power break it a little bit and let off it wants to die. Sometimes it does die. Any ideas? Thanks

 

[mycuda]

Sounds like a vacuum leak somewhere first thought.
Does rpm increase a bunch in park vs drive under load.At idle?

Or idle mixture or float sticking or adjustment needed

 

[Dana67Dart]

My 67 273 with stock 2bbl does some of the same things. Once the eng is warm you can see the clear fuel filter go dry, then the engine drops rpm a bit then the filter fills and the rpm increases. This will repeat till I turn off the engine.
I put a pressure guage on it and right after the filter empties the gague drops from 7 to 4 then refills and goes to 7.

Only thing I can think of is a form of vapor lock from pump to carb and a sticking float

 

[Phil21502]

What’s the best way to check for vacuum leaks?

 

[oldkimmer]

Look, listen. Then spray a water mist around any suspect parts. Kim

 

[RustyRatRod]

Did you adjust the idle mixture screws?

 

[Phil21502]

Yes using a vacuum gauge. Still does it when hot. Just bought a 1”spacer to try. My fuel filter is damn near only an 1/8” off my intake manifold.