Sudden increase in manifold Vacuum? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

5Tractorguy · 07-12-2019, 09:42 AM

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?

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07-12-2019, 09:42 AM	#1
5Tractorguy Registered User Join Date: May 2015 Location: Central Massachusetts Posts: 496	Sudden increase in manifold Vacuum? 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? __________________ Jake 5Tractorguy on Youtube

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