Lumpy idle & 11"Hg, performance cam?

[markolson]

My son's 73 C10 has a relatively new looking Mr. Goodwrench 350 engine in it.  It has long tube headers on it, with Cherry Bomb glasspacks and turndowns, so it is super loud.  It has an Edelbrock high rise intake manifold a a big looking Edelbrock carburetor on it.  It idles relatively smoothly at about 750 RPM, with no hunting idle, but the idle does sound lumpy like it has a performance cam.

We checked the vacuum at idle and it is at 11 "Hg.  I was expecting about 20 "Hg at idle.  We checked some and can't detect any vacuum leaks, although we have not run a smoke test yet.

My thought is that the low vacuum and lumpy idle is an indicator that the cam is not stock.

Am I right or am I crazy?

[zieg85]

could be running rich

[454Man]

You are correct...a cam with that much on over lap wool not have a high vacuum

What's under the hood??? If you have to ask maybe we shouldn't race...

[markolson]

It does smell a bit rich, too.  That might make the idle a bit funky, but wouldn't cause low vacuum.

We have access to a dyno at a local shop, so after a basic tune-up, we plan on using their wideband to dial the AFR in.

I am a lot more familiar with late model Mustangs, which run 20-22"Hg at idle with stock cams, and we see the same on my son's Honda. I was guessing that a stock 350 with stock cams would also see about 20 as well.

Thanks for the validation on the low vacuum. 

[79gmc15]

I get around 13 on my 305 with a comp 268he cam. So you are probably in the right area.

[markolson]

Thanks for the validation.  :beer

[Stewart G Griffin]

Which 350 is this?   The stock 350 goodwrench or the 290hp version?

Where, exactly, do you live?