Another Issue with an Edelbrock 1406

[dznucks]

The 1406 on my 350 has started having new issues recently that have me stumped. The issue is only at idle. Cruise, Power, and WOT modes are perfect, the A/F stays at a pretty steady 12.8-13 throughout.

The idle tune seems to be changing on me and thats where I am .

Here's the typical senerio.....the idle will be typically too rich, A/F 12-12.5, which causes it to be hard to start. I'll get home after work and retune the carb to an idle A/F of 13.5, anything lower than that is too rich and causes a hard start. It will be idling fine, timing is steady at 12deg, vacuum is high at 19" and steady, so i shut it off for the night. the next morning when i go to work, it will fire right up. Once the engine warms and i pull up to a red light, the idle A/F will be 12.5-13. at the next light it may be a steady 13 or it may be 12.5 at the light after that. When i start the truck at lunch or after warm starting it, it idles extremely lean, 16-17, or spiking out above 17, until the truck gets warm. Then the idle A/F goes to 12-12.5. And again at every light it seems to have a different A/F. so, I once again reset the tune when i get home from work, which always ends up with the mixture screws in the same position and the next day its the same story all over again.

I have checked for vacuum leak, i have repeatedly cleaned and blown out the carb, rechecked the float levels, checked the IMS passages, fuel pressure is at 4.5psi, plugs, wires and dizzy (HEI) are all recently replaced and seem to be operating fine. I am running 1" 4-hole carb spacer.

Does anyone have any other suggestions as far as what to check or look for?