How to read carb calibration chart?

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Craig Burriss

Craig Burriss

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Just started driving my car and it runs rich enough to burn your eyes, make the oil smell like gas, and make black clouds when you punch it.
It’s a 70 Duster with an 11.5:1 .030 440, edelbrock performer intake, edelbrock 1813 800cfm carb, see cam specs below, has a mechanical/vacuum advance summit brand electronic distributor, vacuum is unhooked and capped off. 800rpm idle base timing set to 17°, fuel pressure is set to 4psi, fresh 93 octane gas, cheap autolite spark plugs gapped to around .045 because why foul out expensive ones.

I want to get this car running 100% and I can’t figure out this chart I found on the edelbrock website. Can someone please explain to me how to decipher this or give me a recommendation on what I should do?

Chart part1
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Chart part2
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Cam specs
FB47A530-C427-43D3-8DC5-08819DB94673.jpeg


Spark plug after in town driving
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I think that’s everything.
 
Found this video. This makes more sense now. I hope I’ll be able to get it lean enough from this chart
 
Are we to assume this is an automatic transmission car? If so, how much of a drop when you put it in gear? If it's more than about 100 RPM or so, it needs more initial timing. That's the first thing you should rule out before anything else. I saw you said it has 17 initial, but some need more. Also, I think the Autolites are good plugs. Are you 100% SURE on that static compression ratio? Seems like 17* initial is a lot for that. You "should" have problems with spark knock if it has iron heads. If not, I question the compression ratio. Is it MEASURED or is that just what someone "said"?
 
There's another chart that goes along with that for the secondaries as well. Generally when you change the primary setting which that mostly covers do you want to change the secondary setting as well. I know it's rich and all that but how does the car run? and also how do you run it do you idle it alot or do you get on it and really drive it?..
The number one in the middle of the chart is the number one setting... The factory setting. .1113 jets and .068/.047 metering rods.. the first thing I would do would be to not change the Jets and not open up the carb but just try changing the metering rods... The next step leaner is the number 20 setting with the same Jets but 70/54 metering rods.. you can see these rods have bigger numbers which means they are bigger and thicker and more so in theory plugging up the same whole more and allowing less fuel..
When you pull those rods out he'll notice their riding on top of some Springs and those are the Springs are talking about...
I've changed the Springs a couple steps on my carburetors and had dramatic differences in performance with changing those alone...
 
I noticed your cam duration and it looks like 18 to 20 would be a great initial timing.... Do you have vacuum and mechanical advance? And what's your total timing when you have it over like 3 Grand?.. timing is very first thing you want to check but again when you have a performance cam it likes a lot of initial timing to get started.. Factory cams generally are in the 8 to 12 or lower initial timing with vacuum and centrifical advance..
 
Sorry about that I took a second look and yes the vacuum advance so you just have probably in the neighborhood 14 degrees centrifical and you may need even a little bit more initial to get the total timing. Personally I time it for all in and let it back off to what it's going to be for initial. If it's too far out then I start working on widening the curve in the distributor... Meaning of longer-distance I'm timing between initial and all in....
Also once in a great while you'll get something clogged and one of your and let's to your floats and that needle and it allows gas to flood in at all times and makes things extremely rich.. blowing black smoke running terrible and smelling terribly like gas.. check your float needles for trash... I can imagine if they wouldn't close and you're just getting a constant overflow of gas in your carburetor would set off everything...
 
Also just started driving your car? Had it been sitting for a long time? It could be a stuck float stuck down. I've even had one sink as in had a hole in it.. a lot of gas to come flooding in just as if the float needle was clogged or had a piece of trash in it allowing fuel to come in when not wanted..
 
RustyRatRod said:
Are we to assume this is an automatic transmission car? If so, how much of a drop when you put it in gear? If it's more than about 100 RPM or so, it needs more initial timing. That's the first thing you should rule out before anything else. I saw you said it has 17 initial, but some need more. Also, I think the Autolites are good plugs. Are you 100% SURE on that static compression ratio? Seems like 17* initial is a lot for that. You "should" have problems with spark knock if it has iron heads. If not, I question the compression ratio. Is it MEASURED or is that just what someone "said"?
Click to expand...
Sorry, I forgot to mention it’s a manual trans. I got the compression ratio from a CR calculator and assuming that the machine shop that milled the heads told me the cc of the heads truthfully.
 
Craig Burriss said:
Sorry, I forgot to mention it’s a manual trans. I got the compression ratio from a CR calculator and assuming that the machine shop that milled the heads told me the cc of the heads truthfully.
Click to expand...

Understood. I think I would still try a bit more initial timing....."just to see" how it reacts.
 
j par said:
Also just started driving your car? Had it been sitting for a long time? It could be a stuck float stuck down. I've even had one sink as in had a hole in it.. a lot of gas to come flooding in just as if the float needle was clogged or had a piece of trash in it allowing fuel to come in when not wanted..
Click to expand...
Replying to multiple of your posts,
The distributor is vacuum and mechanical, but I don’t have the vacuum hooked up yet, and I don’t know what the advance is at 3k, I set the base at 17 and went with it. I recently got a new timing light though so I can actually figure this out now. The car drives pretty good but looks like a diesel bro at a tractor pull when I think about using the throttle pedal. I had the car running a few years ago but decided to pull the engine to fix some things. The carb sat dry in its box until about a year ago but I’ve started it on a regular basis. I also went through the carb a couple of months ago to make sure it was good to go.
 
Craig Burriss said:
That’s pretty much how I do everything in life... “let’s see what happens if I do this?”
Click to expand...

Sometimes that's the best way. You'd not believe how many of these guys come here for help and go pages and pages and days and days and days and never touch one single thing anyone recommends and yet they just keep right on crying. At least you're DOING SOMETHING.
 
Craig Burriss said:
Vacuum at idle is about 13 to 14hg
Click to expand...

That's pretty decent for that cam, so I'm guessing your timing.....initial anyway is "close". From your description of the black smoke, I'm guessing the carburetor "has issues".
 
Craig Burriss said:
Replying to multiple of your posts,
The distributor is vacuum and mechanical, but I don’t have the vacuum hooked up yet, and I don’t know what the advance is at 3k, I set the base at 17 and went with it. I recently got a new timing light though so I can actually figure this out now. The car drives pretty good but looks like a diesel bro at a tractor pull when I think about using the throttle pedal. I had the car running a few years ago but decided to pull the engine to fix some things. The carb sat dry in its box until about a year ago but I’ve started it on a regular basis. I also went through the carb a couple of months ago to make sure it was good to go.
Click to expand...
with your timing light you'll be able to see where your curve is once it's well warmed up of course you can rub it up to about 3 Grand or so and you can see where the timing will stop advancing and that's your all in or highmark.. and then you can let it drop down to idle and see where it is and that's how much mechanical advance you have... Post Mopar I've came across generally like to be somewhere in the 34 to 36 degrees of advance all In.. your results May vary LOL.. that's what they talk about when they talk about distributor curve.. also how fast it happens... All of these things can be manipulated to make your car run better for your desired driving characteristics... if you're happy with the idea that your float needles are not sticking open for any reason then I would start on the leaning out Trail..
 
RustyRatRod said:
That's pretty decent for that cam, so I'm guessing your timing.....initial anyway is "close". From your description of the black smoke, I'm guessing the carburetor "has issues".
Click to expand...

I would try a step or two lighter springs on the metering rods. If it gets better, you're "going the right way". BUT, there may not be enough "room" with just spring changes. You may need to run bigger metering rods. May even need to re-jet it. Between springs, rods and jets, I don't think there's any doubt you can get it done.

I do think that an A/F meter will help you greatly in this instance. Worthwhile investment for sure.
 
I have to agree my wideband O2 sensor was not only extremely easy to install but helps tremendously with carburetor tuning. Seeing as how I run two carburetors at once it becomes even more tricky... LOL
I think back when I ordered mine they wanted $209 at Summit that they price match for like just under a hundred and fifty bucks for everything..
 
RustyRatRod said:
I would try a step or two lighter springs on the metering rods. If it gets better, you're "going the right way". BUT, there may not be enough "room" with just spring changes. You may need to run bigger metering rods. May even need to re-jet it. Between springs, rods and jets, I don't think there's any doubt you can get it done.

I do think that an A/F meter will help you greatly in this instance. Worthwhile investment for sure.
Click to expand...
j par said:
I have to agree my wideband O2 sensor was not only extremely easy to install but helps tremendously with carburetor tuning. Seeing as how I run two carburetors at once it becomes even more tricky... LOL
I think back when I ordered mine they wanted $209 at Summit that they price match for like just under a hundred and fifty bucks for everything..
Click to expand...
This is perfect timing to install one because I’m about to make a custom gauge cluster with some new gauges. I’ll have to work an AFR in there somewhere. I had one on one of the miatas I had and it was essential in not exploding lol.
 
Craig Burriss said:
This is perfect timing to install one because I’m about to make a custom gauge cluster with some new gauges. I’ll have to work an AFR in there somewhere. I had one on one of the miatas I had and it was essential in not exploding lol.
Click to expand...

They can be an invaluable tool, especially with ethanol laced fuel which makes it difficult at best to read plugs.
 
I’ve learned a lot from this thread. Hopefully sometime this week I can order a few parts and find some time to piddle with it. I’ll come back in here and post what I do.
Thanks guys.
 
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