The Dodge Challenger Message Board

Just a quick question in relation to above.
I purchased a digital timing light with rpm, dwell,advance, etc etc and got to checking the timing today.
I know there is a lot of info on this board in relation to same but after a few beers last night well you know that story.
With the unknown cam in situ the engine seems to idle at its best at around 1100 rpm in neutral.
The damper has no timing tape in place so being 7 1/4" o/d I marked off 1" which should equate to approx 16 degrees and a further mark at 2 1/4" which should be in the region of 36 degrees.
Jiggling around with the dizzy and the vacumn adjuster I ended up with 18 degrees initial at 1100 rpm and 38 total degrees at 3000 rpm.
Both these settings are with the ported vacumn hose in place.
I ran the car out and up to 4000rpm at which point she started to backfire a little.
It would be very rare that the engine would ever see this rpm as it was a test however I would like it to be right so as not to cause any damage.
The above settings are about right I hope but should these be attained with the vacumn hose off and plugged which would result in a higher total when the hose is replaced or am I right with the total I now have with the hose connected.
Cheers
Pat

You are doing it all wrong. Way way wrong.

Let me try explaining a few things again.

At 1100 rpm you are not at idle. You will be on the main jets. This is a bad thing.

To test this put a vacuum gauge on the ported vacuum port which is the one that feeds from above the throttle blades. If you have more than just a hint of vacuum there you are not on the idle circuits. You are on the main jets. The other problem is that your distributor will already be advanced a little mechanically. The car will never drive correctly like this.

Because i don't think you are going to understand how to modify your timing curve in the distributor (at least in the short term) I suggest you try the following.

Plug the vacuum sources for now.

Set the total mechanical timing to 35 degrees at whatever rpm it stops advancing. Usually around 3000rpm-3500rpm.

Now connect the distributor vacuum can to MANIFOLD vacuum. This will be a port on the baseplate of the carb.

This should give you enough advance to get the idle speed down to 800-850rpm. You may have to adjust the idle mixture screws. Test that original timing port for vacuum. There should be zero vacuum on there if you have the throttle blades closed enough.

Now if your engine will not idle at 850rpm or if you cannot get it lean enough it will be because you have a big cam in there.

You will have to open the secondaries a touch if your 4bbl has that adjusment OR drill holes in your throttle blades to allow more air in.

Sometimes you have to go around in circles with this to get it right. It depends how wild the cam is. But getting it right will make it drive like a dream.

Thanks for the quick reply Dave.
This motor runs a Sixpack set up and I aint gonna mess with them boyo,s
I,ll try the other advise and see how I get on.

In that case if you have a big cam you may have to drill holes in the throttle blades to get the blades closed enough at idle. I had to on mine.

This is where I got the 1100 rpm idle setting from Dave.
As I do not wish to get into advance curve weight & spring changes etc I was trying to get in range via the dizzy & vacuum adjustment.
http://tvmoparclub.com/files/tech/Mopar%20Timing.pdf

Before I adjusted anything I got the following readings

At 1100 rpm idle = 22 deg BTDC At 3000rpm = 44 deg BTDC

You driving a Pro Stock car on the street?

No.

Your idle should be 800-850rpm period.

DINGBAT wrote:As I do not wish to get into advance curve weight & spring changes etc I was trying to get in range via the dizzy & vacuum adjustment.:

Yes. Which is why I suggested you do it the way I outlined above.

You HAVE to set the max timing without the vacuum connected otherwise it will be retarded when you don't have any vacuum signal such as when you try to "floor it".

I'm doing my best to help you here but you have to trust me.

DINGBAT wrote:This is where I got the 1100 rpm idle setting from Dave.
As I do not wish to get into advance curve weight & spring changes etc I was trying to get in range via the dizzy & vacuum adjustment.
http://tvmoparclub.com/files/tech/Mopar%20Timing.pdf

Before I adjusted anything I got the following readings

At 1100 rpm idle = 22 deg BTDC At 3000rpm = 44 deg BTDC

Dave my apologies if this post was miss leading.
The above is what I had been fiddling around with prior to your reply last night it is in no way being derogatory toward your good self.
I intend to change the set up per your advise which I value.
I,ll stand you a beer or two at the Pod
Best Regards
Pat

If you get it to the Nats I will have a look at it for you.

Dave I disconnected the dizzy vac hose and blanked same.
Set idle at 850rpm and advanced the dizzy and kept adjusting the idle to 850rpm to attain 16 deg initial and 32-33 degrees full at 3000-3300rpm.
The blanked inlet I assume is the ported vacuum but any other ports seem to be in use ie from the base of the centre carb to the breather. The port on the other side of the manifold is servicing the Brake servo I cannot see any others. Am I missing something obvious like that breather pipe should run to the base of the air filter or am I still making a dogs of it.
Pat

You need to advance the distributor just two degrees more.

If you have 16 degrees initial at 850rpm already then it sounds as if you already have a modified distributor. If you advance it to 18 or 19 degrees initial that might be enough and you will not need vacuum advance at all. Or at least only 5-10 degrees of vacuum at most.

But the manifold port is under the center carb fuel bowl if you need it.