Idle Problems?

[fried_guy]

Ok, so I got my engine assembled and running.

No vacuum leaks, oil leaks, smoke, smells, odd noises, overheating, surging, etc... the only problem is my idle quality.......I think .

Here's my combo:
406 SBC
5.7" Rods
9.1:1 compression ratio with 30cc dish KB pistons
670 Truck Avenger
Comp Cams Extreme 4x4 12-243-3 (270/278, 227/235, .480/.498, 111)
IE 200cc heads with the exhaust cleaned up
high performance ignition system
fully balanced and blueprinted
All new parts except for the block
all the bells and whistles, etc, etc, etc.

I can get it to idle at around 800RPM in neutral, but it's not the smoothest idle. Pulls 16"-17" of vacuum in neutral. Haven't checked it in gear.

Messed with the timing a bunch... doesn't seem to have much of an affect after around 18 degrees. Using vacuum advance on full source.

I tuned my idle mixtures properly... but they seem a little off. They really have almost no affect on the vacuum or idle quality unless I lean them out too much and it stalls. On most of the other engines I've worked on, adjusting the idle mixture screws seems to make a significant change in the vacuum. It seems that with this setup it's either too lean, or ok. No in between.

The vacuum seems good, but doesn't the idle speed seem a tad high?

Here's the only problems I can see:
1. I converted a dead head regulator into a flow through
-at idle the pressure fluctuates rapidly between 3-5psi
2. Using stock exhaust system
-don't know if it's clogged or how restrictive it is
3. Carb problems
-needs to be cleaned/modified?
4. I'm totally trippin'
-this is to be expected with the combo....

Any input would be great
Thanks in advance,
Casey

 

[corey6969]

I think its the profile of the cam is why u get the kind of choppy idle. I know on the high energy cams the 270 duration cams have a bit of a choppy idle. Here is a link to the specs for your cam http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=97&sb=2

16-17 inches sounds good for that cam so I think you good to go with the cool choppy idle. I have an extreme energy cam in my 406 and the valve train is a little noisey, but I love the cam.

If you exhaust is to restrictive you will see it on your vacuum gauge, the vacuum will drop, if its to clogged it could go to 0. Fuel pressure will fluctuate with a mechanical pump so that seems normal. And hell ya its an awsome combo, mines pretty much the same as yours and how can i say TORQUE MONSTER!!. Also I have a holley street avenger carb, pretty much the same as the truck avenger, they can be screwy carbs, are you able to get the idle below 800?

 

[fried_guy]

Thanks Corey!

I cleaned and rebuilt the carb and adjusted the transfer slot by opening the secondaries a little, and tightened the manifold a little more... able to idle IN GEAR at around 500-600. Considerably tamed it. My battery and gas can (i'm using as a fuel tank until i get mine cleaned) are on the ground, so I couldn't move it more than a few inches... but DAMN.

I'm getting around 14 inches of vacuum in gear. Steady.

I can't wait to get my battery tray so I can mount that thing and use my fuel tank...

Even with my old exhaust system (with junk mufflers) and manifolds, it sounds pretty good... it'll be great when I get my mandrel bent x-tube exhaust and headers installed too!

 

[corey6969]

Sounds like ya got er runnin good now, ull love it when ur able to move it!