Thread: 396 Rough Running

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I just rebuild a stock 396 and it is running very off. It won't idle unless I advance the timing to 20 degrees and then the vacuum is only 14". The compression is even, cam timing good and the intake seems leak tight. I runs like the cam timing is off or there is a vacuum leak but I cannot find anything wrong. It has a factory 350 hp cam with about 215 degrees of duration (mild).

Any ideas??

How is your distributor? I had a similiar problem with a 350 and after going crazy over it, I changed the distributor. I had previously replaced the module, rotor, cap, wires, plugs, tweaked the carb over and over. Changed the PVC, EGR, checked all the hoses, changed idle speed, low speed fuel adjustment, I just went nuts.
Got desperate, threw in a new distributor, and problem solved!
I hope it is that simple.
A .214 cam is pretty mild, and vaccum should not be an issue. Might be off a tooth in the chain also. One thing I had once, I had a valve cover that did not seal well at all. It was at the top of the cover and it let too much air into the crankcase. The carb ran way too lean.
Good luck.

The PVC was dumping into the carb. I had gotten cast valve covers, and there was a casting defect near the PVC valve.
I replaced the valve cover with steel and problem solved. It ran like it had a vaccum leak.
It was not like a gasket seep, I found the casting defect after changing the covers.

Geodude, I would look toward ignition timing. You mention that the "cam timing is good" but then you say that might be your problem. Which is it?? How do you know it's good?? I doubt that's your problem, it would have to be way more than a tooth off to run that bad. But ignition timing is definitely a possibility. Start over with the timing, make sure it's advanced enough, and check to see that it's hooked up right. Did you mess with the carb at all? Is it the same one you used before, and how did it run before? And Docone31, no offense meant, and I think someone is hinting at this in another way, but valve covers have nothing at all to do with how an engine runs. Think about it, it makes no sense.

I know it sounds unlikely, something like greasing the framistan, but it happened.
Bear with me, back then I was a little green. I had a quadrajet and had rebuilt it for the first time. All went well. I got those valve covers at a fleamarket and rushed to put them on. Untill I changed the valve covers, the engine ran miserably. It ran like it had a vaccum leak.
I was just trying to help, like I had been helped with my issue with my van. You guys really helped me out. If I appear off the page, I am sorry.
I am also aware that the PVC line cannot be run open. Back when we first started fooling around, we would take the PVC line off the carb and it would act lean.
At any rate, I take you guys pretty seriously. I have learned a lot since then. I still take care to make sure my PVC valve and hoses are intact. Maybe it was one of those things, but it happened to me. I still try to figuire out alternatives. I removed the front two plug wires to remove the valve cover on each side. I put them back correctly. There was nothing else that could have been messed up. It was an early '70's camaro and it had no smog gear. I deducted it was a vaccum leak from the crack being so close to the PVC valve. Too much air flow.
I donno. I tried anyway.