Edelbrock Performer idle mixture tweaking

[Dr. Righteous]

Ok, this is continued from RED HOT HEADERS
Here is what went into my 383

'71 383 truck motor
Bored .030 over
stock (freshened up) heads milled .020 (used MP steel shim head gasket)
KB Silv-O-Lite .030 overbore flat top pistons
Speed Pro moly rings (specially gapped for the KB pistons)
Edelbrock double roller timing chain set stright up (not advanced or retarded)
CraneCams #H-272-2 dual pattern cam and lifters
Advertised duration/lift
intake: 272*/.454
exhaust: 284*/.480
Edelbrock Performer RPM intake
Edelbrock Performer Carb #1407 (added elect.choke option)
JR street headers
High pressure spring in oil pump.
MP performance electronic iginition conversion kit
Accel 8mm wires and coil
base timing 10* (MP book said 5* but it wouldn't idle right)
It pulls around 14 inches of vacuum at idle
The vacuum advance is on ported advance (the left front port of the carb)
NOW, if you are wondering what my Compression ratio turned out to be; I don't know.
The stock compression on that engine was 8.7:1
The KB pistons reach TDC even with the deck height as the stock pistons didn't.
A compression test reads 150 PSI
That should be close to where I need to be with that cam.
Now, Mind you that this engine is FRESH. No miles on it accept garage running to tweak it.
I am still missing the correct brackets for the power steering pump before I can drive it and it has open headers right now. My neightbors are not too understanding since most of them are retired folk.
It seems I cannot get an Idle mixture that is not so lean that the headers get extremely hot or so rich that it stinks too much.
I am still a novice when it comes to performance tuning and modifed engines.
(I have been away from MoPars for many years)
What do you guys think of my build up and what changes would you make for a potent street driven car like this?
I don't know what to think about the information that accompanied the iginition set because it is somewhat vague. I think what is in there doesn't apply if you have done any modifications to your engine.

One other note. I advanced the base timing from 5* to 10*. This seemed to help its idle quality. Right now it seems to run a little rich. I have not tweaked the mixture much since I cannot get it better.
When the base timing was set to 5* and the mixture was set where the exhaust didn't stink because it was so rich the engine temp would rise pretty quick.

Any ideas or suggestions would help.
Thanks guys!

[Mopar_Maniac]

What is your idle speed? If it is too high it might be that your not in the idle circut.

Initial timing at 10* is a good starting point. What did you set the gap at on the distributer?
Remember, set dist. gap first, then set idle speed, then set timing. If you change the dist. gap it will change the others. Your best bet is to start over.
set dist. gap, set timing, set idle speed, recheck timing and adjust if needed. Any time you adjust timing, you must go back and reset idle speed. Make sure you plug the dist. advance before setting timing.
Adjust idle mixture screw's for either highest vacuum reading, or idle speed. Reset idle speed and recheck everything again.
It is mostly trial and error. Very easy, but very time intensive if done properly.

Later,
Jeff C.

[Dr. Righteous]

One question. What do you mean by distributor gap? You can't mean point gap, its electronic. The stator/pickup gap is set to the MP spec. Is that what you mean?
I know its mostly trail and error because different setups behave differently. Whats funny is that changing the idle mixture doesn't affect vacuum or RPM much until you just about seat the screw. There isn't much tunability. Idle speed is around 750 RPM.

[Mopar_Maniac]

Yes...I was talking about the pickup gap.

Have you set "total advance", or just initial?
The reason I ask is this, Mopar Performance states "in performance situations, total timing is always set, not initial timing."

In the 8th edition of Mopar Engines they recommend 38 degree's total. They also say that all Mopar Performance dist. are recurved and are "all in" at 2000rpm.

On to the carb mixture problem.
You say that you don't notice any changes until you have the screw's almost seated. That makes me believe that possibly your idle metering rod's are too rich? You are leaning out the mixture by turning them in, so it sounds like you are running too rich.

Of course, you could just have a vacuum leak causing the mixture problem. I'd much rather see the car in person than try and do diagnosis over the internet. Abviously that won't work, but it would be nice.

Good luck, and let me know if it works.

Later,
Jeff C.

[LA360Dart]

My 2 cents Dr. Righteous your problem is a common one with the #1407 Edelbrock carburetor your mixture screws need to be screwed out to richen the idle mixture. The open headers are not helping the tuning situation get an exhaust system. Techs at Edelbrock tell me that the boosters have a tube orifice that should be .037 at minimum some Mopars, have had to increase this to .041 to get idle quality, Get exhaust first to allow you to tune the setup
Denny

[Dr. Righteous]

I considered the absents of an exhaust system would affect tunability.
Well, I have done a little more tweaking and it is somewhat better than it was. I will do it again once the exhaust system is on the car.
Thanks Guys

[Dr. Righteous]

One question I have is that with the combination below (first post in this thread)
and a compression reading of 150 PSI, what should my final compression ratio be?