Sudden increase in manifold Vacuum?

[5Tractorguy]

For some reason the 350 in my '77 GMC started running a bit rich a few weeks ago. I noticed that the vacuum gauge is reading about 2-4 higher than usual. Any idea what would cause this? I pulled the top of the carburetor (Edelbrock 4 barrel) and cleaned/blew everything out (no difference). Nothing noticeably dirty inside... May pull it completely off to clean. Maybe something with the PCV valve??

It was running fine (even after sitting all winter) until I started it one day and noticed the difference. Any thoughts?

[Dead Parrot]

Verified reading with 2nd gauge?
Timing moved to more advanced, either from loose dizzy or stuck mechanical.
Idle mix was too lean to start with and the more rich increased idle speed and vacuum.

You can do a partial cleaning without pulling the carb. Loosen the power piston covers and pull the pistons and rods. Give the pistons and cylinders a good spray down with carb cleaner. It doesn't take much evaporated gas goo to keep those from moving properly. Same with unscrewing the idle mix screws and making sure those are clean.

[5Tractorguy]

Originally Posted by Dead Parrot

Verified reading with 2nd gauge?
Timing moved to more advanced, either from loose dizzy or stuck mechanical.
Idle mix was too lean to start with and the more rich increased idle speed and vacuum.

You can do a partial cleaning without pulling the carb. Loosen the power piston covers and pull the pistons and rods. Give the pistons and cylinders a good spray down with carb cleaner. It doesn't take much evaporated gas goo to keep those from moving properly. Same with unscrewing the idle mix screws and making sure those are clean.

Thanks, I'll give that a shot and see what happens! I figured it has to be something simple since it was okay the day before. Probably has a piece of crap caught in it somewhere...