ironhead88

I have been trying to tune my carbed 327, and it seems like it runs okay, considering that I'm just beginning to get this build dialed in.
The build is close to stock with a 204@.050" cam and 8.6:1 CR and shorty headers. I have a Quadrajet and an HEI
I have been getting the feeling that I made an error when I was setting up my timing pointer to it's mark, because it seems to idle best at 45deg advanced with manifold vacuum hose attached.
So just to keep things moving along, I remembered something I was told; and that was, if you don't have a timing light, you can set the idle advance with a vaccum gauge by turning it to the point where it's at max vacuum.
Well I did that, and then double checked it with a light and it's still wanting to idle at 45deg.
So until I re calibrate my timing marks, i'm playing it by ear... or by smell.
So ignoring the #s ... I'm getting a smell from the exhaust that makes my eyes water and burns my nostrils.
I leaned the mixture... When it's running rich, it smells like the choke is on, sort of.
What is it an indication of (timing-wise) when the exhaust burns your eyes? Anything?
I'm just viewing this as an educational experience for now
It's good to know of alternative methods when the #s don't seem right

Thanks

zed-028

While we wait for Sofakingdom's response (this one is right up his alley)

1. get the car warm
2. disconnect the vac hose
3. set the base timing so that the engine will run probably 0 degrees or whatever the stock number was (forget the idle quality for now)
4. screw the air bleed screws on either side of the carb inwards gently until they begin to bottom out, then back out about 2-3 turns (youll probably have to increase the Idle screw at the same time or it will conk out)
5. turn the air bleed screws counter clockwise bit by bit and you should hear the idle increase (you may have to screw out the idle screw at the same time) - when it stops increasing thats about the sweet spot
6. use the idle screw to set the appropriate idle (sticker above your head under the hood)
7. reconnect the vac hose and confirm the idle speed is correct.

Thats the base point of running the car, the rest of the tune is by feel and hearing. Take it for a run, plant your foot, if it feels like it could go a bit more timing, get out advance it slightly, boot it again - if it can go more, give it more timing, if it pings then back it off a bit. All the while you will have to make minor adjustments to the idle screw or you risk having some run-on/dieseling.

also - after all this you may find yourself having to re-set the secondary air door spring - its less daunting than it sounds but theres plenty of info on here to help you out

zed-028

After re-reading i imagine your timing tab is off. 45 degrees sound much more like a total timing figure as opposed to a base one. In that case - if the idle feels good at that timing then it is good. Play with the carb tuning from there

ironhead88

Thanks for that info - That's helpful
I've been doing that, It seems to be a sensible approach, but it's good to hear a second opinion.
The smell is bothering me. It's really an irritating smell at idle - Burning eyes
As I mentioned earlier, this is a good learning experience for me, because not being to rely on the numbers due to my timing marks being off, it forces me to get more real with what's going on.

What I have done is basically as you described;
I advance the distributor til the idle quality is good enough for the engine to idle fairly smoothly, and no further than that. At that point the vac gauge is just getting to 16"
If it's retarded any lower than that the vac gauge drops and the engine chugs and wants to die.
So when I get to that point I begin adjusting idle mix and speed...
But no matter whether the idle mix screws are lean or rich, the exhaust stinks

I'm looking forward to getting to the point where the primary is adjusted and its time to play with the secondaries!

Tibo

iTrader: (15)

Am I reading this right that you have a 327 with a stock-ish cam and you are running 45° advance at idle? You should be using half that amount of advance. You're probably running almost entirely off of spark advance. When you are starting it up from a cold start are you having long crankings?

ironhead88

After reading a few replies here, it became clear to me that I needed to double check my work.
I thought it was the timing marks, at first, but I believe that some plug wires were out of sequence.
Amazingly the engine ran smoothly but it had a tendency to ping - BAD - I thought I had dropped a piece of hardware down the intake.
And the exhaust smelled like formaldehyde
So I disassembled the ignition - Double checked timing marks - Didn't ever find out what I actually did wrong, which frustrates me
But when I reassembled it everything was fine.

Thanks for contributing