Cliff's Quadrajet Parts and Rebuild Kits

Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: bruno on March 23, 2026, 02:42:06 PM

Title: will a pcv valve cause a lean condition?
Post by: bruno on March 23, 2026, 02:42:06 PM

long story short, I’m having trouble with what i think is a lean bog right off idle. 68 chevelle 396, mild cam. idle vac. is 18, steady. timing is 10 initial, another 10 from manifold VA, centrifugal starts at 950ish, adding another 26 at 3600ish. it idles well, both mixture screws have response, they’re set at 3 turns out. accelerator pump has a good shot in both primaries. idle tubes are .037, DCR is 052, LIAB is 063, UIAB is 070. holes under i’ll screws are 085. I think i should have lots of idle fuel. when i pull th pcv valve and block it off, the rpms drop about 50, and the bog nearly disappears. should the pcv be flowing a ton of air at idle? it is connected to manifold vacuum at the front of the base plate. I did replace this pcv a while ago from napa, so it SHOULD be the correct one. I also have an air cleaner base that has a spot for a pvc hose, would that be a better option?

Title: Re: will a pcv valve cause a lean condition?
Post by: bruno on March 23, 2026, 02:42:57 PM

sorry i forgot, Idle bypass air is 095.

Title: Re: will a pcv valve cause a lean condition?
Post by: bruno on March 23, 2026, 06:53:13 PM

well it seems like an adjustment to the APT cured the bog. the tip in caused a 50 rpm increase now.