Black soot on ground at start up

[Davison]

1972 440-4 automatic: For a cold start, I press the accelerator once to the floor, turn the key and the car starts right up. However at the exhaust, there's black soot on the garage floor. This soot does not happen on a warm start, nor is there any soot coming out of the exhaust when the car sits at idle for a few minutes. No soot or smoke when driving. Would the solution to reduce or eliminate the soot be to set the choke a bit to the lean side? Any other suggestions? Thanks.

 

[slimt]

1972 440-4 automatic: For a cold start, I press the accelerator once to the floor, turn the key and the car starts right up. However at the exhaust, there's black soot on the garage floor. This soot does not happen on a warm start, nor is there any soot coming out of the exhaust when the car sits at idle for a few minutes. No soot or smoke when driving. Would the solution to reduce or eliminate the soot be to set the choke a bit to the lean side? Any other suggestions? Thanks.

you should see the inside of my garage door. Two big black eyes. Mine burns lean.

 

[68Moparmaniac]

You didn't mention what kind of carb your running. If it's a Holley then your pretty much gonna have to live with your eyes and nose burning. You can tinker with it to get it better but you'll be having a winter and summer choke settings respectfully. Every Holley I've had runs a little fat when cold but leans out when your temps come up, kinda the nature of the beast.

 

[Davison]

Yes, it is the original Holley carburetor that the car was built with. It has been rebuilt and runs very well, except for the soot at start up. The car only runs in warm weather, the start up is at above 60 degrees. That is what I keep the garage at.

 

[68Moparmaniac]

Yes, it is the original Holley carburetor that the car was built with. It has been rebuilt and runs very well, except for the soot at start up. The car only runs in warm weather, the start up is at above 60 degrees. That is what I keep the garage at.

Then really all you can do is work on the choke and idle circuit

 

[Davison]

Then really all you can do is work on the choke and idle circuit

Ok, Thanks. Appreciate the input. It's a minor nuisance, so i guess i will live with it.

 

[myk r sanchez]

You didn't mention what kind of carb your running. If it's a Holley then your pretty much gonna have to live with your eyes and nose burning. You can tinker with it to get it better but you'll be having a winter and summer choke settings respectfully. Every Holley I've had runs a little fat when cold but leans out when your temps come up, kinda the nature of the beast.

I have to wonder, were these cars like that when they were new?

 

[dual fours]

I have to wonder, were these cars like that when they were new?

If I remember back, at times (it may have been a seasonal/temperature thing), I had moisture mixed with the black spots on the back wall. The running make-up look. Using the highest octane gas I could afford at the time. With a Carter carb.

 

[Cranky]

Also a cold start quickly creates moisture in the exhaust system and this will cause the spits so to speak. Being rich just makes it worse. And it seems like a straight pipe system is even worse....

 

[dual fours]

Also a cold start quickly creates moisture in the exhaust system and this will cause the spits so to speak. Being rich just makes it worse. And it seems like a straight pipe system is even worse....

That makes sense, I was Rich and Straight.

 

[Ed Martin]

1972 440-4 automatic: For a cold start, I press the accelerator once to the floor, turn the key and the car starts right up. However at the exhaust, there's black soot on the garage floor. This soot does not happen on a warm start, nor is there any soot coming out of the exhaust when the car sits at idle for a few minutes. No soot or smoke when driving. Would the solution to reduce or eliminate the soot be to set the choke a bit to the lean side? Any other suggestions? Thanks.

I ran across your posting (including the response from others) when I was getting ready to post the same issue with a picture I just took of the black carbon deposits at the tailpipes of my 68 Roadrunner. I installed a new Holley 600 cfm carb in Nov 2018. Previously, I had another Holley for many years without this kind of problem. And it did not do this until I made some adjustments to keep the choke fast idle to stay on longer by rotating the choke several notches CCW. Have you done anything more to fix your problem? Did your problem just start recently or has it been there all along? I also thought the choke adjustment may have something to do with it. I cannot get the choke plate to move when I loosen and rotate the a black cap as they describe in the first minute of this YouTube (). I'm wondering if the black soot is due to the choke being closed too much on startup, but can't figure how to adjust it.

 

[coloradodave]

Make sure the throttle is open and the choke fast idle is clear of the adjustment screw before you turn the black cap. In other words, make sure the choke blade will 'flop' around before adjusting the cap. Then adjust 1 notch at a time toward less tension on the blade. Drive the car until fully warmed up. The less the choke stays on, the better...

 

[Ed Martin]

Make sure the throttle is open and the choke fast idle is clear of the adjustment screw before you turn the black cap. In other words, make sure the choke blade will 'flop' around before adjusting the cap. Then adjust 1 notch at a time toward less tension on the blade. Drive the car until fully warmed up. The less the choke stays on, the better...

Thanks coloradodave. I think what you're talking about is to make sure the fast idle adjustment screw is not in contact with the red fast idle cam when trying to rotate the cap. It seems there may not be a good solution if you have both black soot at startup (where I understand the cap should be rotated CW to fix by allowing the choke to increase air flow at startup) and also have the fast idle coming off too soon (where the cap should be rotated CCW to fix). How can the adjustment be made to fix both problems?
Also, isn't there a vacuum pull to open the choke a small amount from closed position on startup before the bimetallic spring in the choke starts to heat up? I though my old Holley had this.

 

[toolmanmike]

Your carb can be set lean for idle and main metering but rich for choke operation. That's where the black comes from mixed with a little moisture in the exhaust. I like a little fast idle so I set my choke rich enough to get that. There's not much tension on the butterfly when started cold.

 

[coloradodave]

As a test to see if the choke is causing your problem, adjust the cap with enough tension that it is full open, even when cold. You can even wire it open. You may have to let the engine warm up a bit before driving, depending on the weather, but if the black soot problem goes away after several days of driving without the choke engaging, at least you'll know you're working on the right problem.

 

[Ed Martin]

As a test to see if the choke is causing your problem, adjust the cap with enough tension that it is full open, even when cold. You can even wire it open. You may have to let the engine warm up a bit before driving, depending on the weather, but if the black soot problem goes away after several days of driving without the choke engaging, at least you'll know you're working on the right problem.

Does the throttle have to be fully open (and kept open) while rotating the cap? Yesterday I tried it again and opened the throttle enough to let the plate close completely, but could not get the plate to open at all by turning the cap (I didn't want to open fully and squirt gas without starting it up). I could not see any mark on the cap to know the range of notches (on the metal part) to stay within when rotating the cap (I will look again). When I cracked the throttle, there was a fair amount of tension holding the plate closed. From when I put the carb on new (a year ago), I've rotated the cap a total 8 notches CCW to keep fast idle on longer but now have rotated it back by 5 notches CW to try to get rid of the black soot (but it is still is there on my last drive). Thanks so much!

 

[toolmanmike]

When I cracked the throttle, there was a fair amount of tension holding the plate closed.

There is your problem. It is set too rich if it has a lot of tension. The choke coil is just supposed to close the choke plate when started cold. It should have just a little tension when it it closed. It should "just close". And, setting the choke richer won't make the fast idle stay on longer. The fast idle cam pivots on a screw and is a counterweight. Pump the gas pedal and the cam turns with gravity and will stay in the fast idle position forever until you tap the gas to allow it to spin to curb idle position.

 

[Ed Martin]

There is your problem. It is set too rich if it has a lot of tension. The choke coil is just supposed to close the choke plate when started cold. It should have just a little tension when it it closed. It should "just close". And, setting the choke richer won't make the fast idle stay on longer. The fast idle cam pivots on a screw and is a counterweight. Pump the gas pedal and the cam turns with gravity and will stay in the fast idle position forever until you tap the gas to allow it to spin to curb idle position.

This is very helpful information. I will have to look at it some more. Do you have to open the throttle completely to make adjustments by rotating the cap? Without an indicator mark on the cap (other tan what I made for reference, cause I cannot tell where it was set when new). I'm afraid I might turn the cap too far out of its range and damage the bimetallic spring, as they warn you not to do.

 

[toolmanmike]

This is very helpful information. I will have to look at it some more. Do you have to open the throttle completely to make adjustments by rotating the cap? Without an indicator mark on the cap (other tan what I made for reference, cause I cannot tell where it was set when new). I'm afraid I might turn the cap too far out of its range and damage the bimetallic spring, as they warn you not to do.

You can rotate the cap at any time. When you adjust the choke cap you can back it off until the butterfly opens and turn it the other way until it just closes. Mine is probably set a notch or two rich from the "just closed" position. Once you get it close, you can adjust a notch at a time to get it just right. Too lean and you may not get enough choke or fast idle. Too much and you are blowing black smoke like you are experiencing. One notch is probably a 1/16".

 

[coloradodave]

Another video. Very clear directions. Also works for non electric chokes.
https://www.google.com/search?q=how...US751&oq=how+to+adjust+the+electric+choke+on+