Surges at idle and steady RPM

[grandpaslincoln]

I came home from Wal-Mart last night, everything was fine. Started it today, and now the engine is surging pretty bad at idle, and when you hold it at any steady RPM, it surges but not as bad. Surges worse in gear. Normal vacuum reads around 15 at idle, right now it's about at 12 or so. I checked for vacuum leaks, none found so far. What else could it be?

Just for a refresher for those who don't know or forgot:

2150 2bbl
Duraspark 2 conversion

[gadget73]

vacuum leakage or late timing? 15 is low. Should be able to hold 17 or better at idle. Did you try the carb cleaner around the manifold edges and at the carb base trick?

[grandpaslincoln]

15-16 has always been normal, it'll go up to 17 every once in a while. Haven't tried the carb spray trick, guess I'll have to get some.

[p71towny]

Leaky brake booster??? There's a leak somewhar.

[grandpaslincoln]

Tried the brake cleaner around the carburetor base gasket trick. Instantly ran smoother when I sprayed under the front side. Also instantly ate the paint off the intake, but that's no big deal. So new carb base gaskets are in order. Thanks for the suggestion Thain mang!