Originally Posted by killerformula
Thanks for the comprehensive reply. I'm not entirely sold on the percolation issue, especially since I get the problem even only running a couple minutes. That said, I certainly do have an insulator I could install and it costs me nothing to at least try it!
Percolation is common- just ask any Edelbrock carb owner. Holley not so much. Aluminum carbs are worse about this than zinc castings, after there are more aluminum Holleys out there we'll see if that changes. But if the same thing happens even after a short run, I agree percolation isn't the problem.
If the fuel pressure is too high for the needle and seat, the bowls can overfill after the engine is shut off while there's still pressure in the fuel line. If this is happening you should be able to run the engine, shut it off, then wait a few minutes until it starts to seep before remove the sight plugs to see if the fuel level has risen a lot. If you have side hung float bowls connected w/the balance tube, removing just one plug will tell the story.
This doesn't necessarily
mean the fuel pressure is too high, just that it may be too high for the needle and seat/float the way things sit. The float might be heavy or the N&S assembly worn or has a spec of dirt, etc. fouling it.
See what that tells you, if anything. If that's not it we'll keep trying.