Black Smoke, have to screw idle/air all the way down

[ubtripn]

I have a fairly new 350 - was told it was a 383 stroker but it started life with me as a mystery crate engine I got for next to nothing. Anyway, at idle it was leaving black soot on the curb. So I thought it's running rich. It has an 800 Edlebrock so I think it is probably overcarbed but I went through the air/idle tuning by turning the 2 screws all the way out then back in until it is where it should be. Problem got worse, I only got it to improve when I turned the screws all the way clockwise. Strong, instant throttle response as before but no soot at idle or black smoke. BUT When revved fast I still get black puff of smoke which I think is unburned fuel.

Anyway, I read that running too lean is damaging so I backed each screw one half turn back from fully seated. Runs fine, does not smell like gas unless I put my foot in it when I get the black smoke so I basically got most of what I wanted until I can carb it with what I want.

The question is, is it even possible that I am running too lean right now? How can I be getting any black smoke when hitting the throttle hard if both screws are fully down?

I am not that great with carbs, if I keep my foot out of it I got what I want but I need your opinions, thanks folks.

My main concern is that I am not damaging the engine running this way or too lean, it does not act lean, thanks.

[BugzC10]

Does your carb have automatic or manual choke? Is the choke fully open after warming up?

[custom10nut]

The idle mixture screws on the base plate of an AFB Carburator (Carter/Edelbrock) are for idle only. As soon as you hit the accelerator that part of the operation stops and your accelerator pump takes over. For the longest time I was under the impression that those screws effected everything from acceleration the gas mileage. Until someone on this forum explained it to me. I you're running rich or lean, it's from improper jets, needle valves, or (needle)valve springs. The Edelbrock carbs usually come pretty close to set out of the box, and sometimes or own desire to "improve performance" hurts it more than helps. I just read the size, and I agree, it's a tad big for a fairly stock 350

[cdowns]

do you have a properly installed PVC system

[ubtripn]

I do have a good pvc system.

I have a manual choke I never need to open.

I thought the accellerator pump sends a pre-shot in before the main stream to provide no delay of the line, is this incorrect?

The idle screw is on the bottom of the linkage, it moves in or out affecting resting idle. During this whole adjustment on the two front screws the idle never changed.

[Jack_71C10]

I had the same problem with my edelbrock carb.
Turned out to be my fuel pump was putting a little too much pressure
for the carb. I could close the needle valves and it would still run
because the float wouldnt close and the bowls would overflow.
I installed a fuel pressure regulater, retuned the carb and
now it runs great.

[RichardJ]

You wrote curb and I misread that as carb.

Check for bad or poorly adjusted float.

[geezer#99]

[QUOTE=ubtripn;7592840]I have a fairly new 350 - was told it was a 383 stroker but it started life with me as a mystery crate engine I got for next to nothing. Anyway, at idle it was leaving black soot on the curb. So I thought it's running rich. It has an 800 Edlebrock so I think it is probably overcarbed but I went through the air/idle tuning by turning the 2 screws all the way out then back in until it is where it should be. Problem got worse, I only got it to improve when I turned the screws all the way clockwise. Strong, instant throttle response as before but no soot at idle or black smoke. BUT When revved fast I still get black puff of smoke which I think is unburned fuel.

Anyway, I read that running too lean is damaging so I backed each screw one half turn back from fully seated. Runs fine, does not smell like gas unless I put my foot in it when I get the black smoke so I basically got most of what I wanted until I can carb it with what I want.

The question is, is it even possible that I am running too lean right now? How can I be getting any black smoke when hitting the throttle hard if both screws are fully down?

I am not that great with carbs, if I keep my foot out of it I got what I want but I need your opinions, thanks folks.

My main concern is that I am not damaging the engine running this way or too lean, it does not act lean, thanks.[/QUOT

You need a fuel regulator set at 5 psi.
Too much pressure is making your carb flood.
That's the cause of the black smoke when you wack it.
Turning the screws in all the way with no reaction tells you that you have the idle set to high on the carb. You're idling on the power circuit. You need to close the throttle back down to cover the transition slot.
Look here for info on that.
It's for a holley but your carb is the same.
http://www.crankshaftcoalition.com/w...EI_distributor

A way to get it to idle well enough without opening the idle too much is maximize your initial timing and/or hook your vac pot to manifold vacuum.
Your initial might need to be upwards of 20 degrees.

[snj8198]

You stated you are running a manual choke. I take it that this is a standard Performer series 1412 800cfm? You may have your idle adjustment turned up too high uncovering too much of the idle transfer slot causing the motor to pull directly from the primary circuit at idle.

-check your floats, the adjustments are: 7/16" from bottom of the horn, and 15/16-1" full droop.
-check your fuel pressure: should be 4.5-5.5psi.
-check your pump squirter rod adjustment, it may be too much initial squirt for your motor.
-what intake are you using?
-how much vacuum are you pulling at idle?
-what's your timing at idle? you need as much initial as possible plus full manifold vac adv.
-what calibration chart # are you at for your primaries? (both cruise and power mode)
-what transition springs are you using?


lot's of questions but i think we can get it straightened out.

Steve

[ubtripn]

Thank you all VERY MUCH. Now I have a couple angles of attach which is what I needed.

[ubtripn]

Does a fuel pressure regulator also help a little with MPG? I get like 7mpg.

[ubtripn]

I will gather as much info on my set-up as I can. I think the pressure regulator is a good start. Once we start getting into things like transistion slot I am lost =) BUT, I am going to study up.

[geezer#99]

Originally Posted by ubtripn

Does a fuel pressure regulator also help a little with MPG? I get like 7mpg.

In theory it should since you're not wasting fuel, but in actuality it'll likely be the same due to your replacement of that black smoke out the back with white tire smoke!!

Honestly it should help but your timing will help the most.

Don't dwell on the transition slot.
If you get your timing cranked up, your idle turned down and your mix screws working right, you'll know the transition slot is covered.

[ubtripn]

Thank yo very much!

[long67]

Black smoke is from it running to rich,carb is to big.

[ubtripn]

Yes it is, Gezze#99 did you mean 20 degrees BTDC?

[geezer#99]

Yupper!!
Depending on the rowdiness of your cam plus your 2500 foot elevation needs lots of initial.
Start off at 16 and experiment. Bump it up 2 degrees at a time until it cranks hard hot then pull it back a couple degrees.

Don't worry about your carb being too big. It's just the right size for a 383.

[ubtripn]

Sounds good and thank you very much. Quick question, my mechanical fuel pump is new, is it possible the output is too high since it is mechanical? Shouldn't it be 4-7 psi? Only asking because I am thinking of retiming tonight after backing my idle down to get out of the power circuit mode like you said but I am not sure if I should install a fuel pressure regulator first since the good ones run around $100 when considering hoses, etc..

[ubtripn]

SNJ8198 - I am working on my nomenclature so I can check those specs, thank you!

[geezer#99]

Originally Posted by ubtripn

Sounds good and thank you very much. Quick question, my mechanical fuel pump is new, is it possible the output is too high since it is mechanical? Shouldn't it be 4-7 psi? Only asking because I am thinking of retiming tonight after backing my idle down to get out of the power circuit mode like you said but I am not sure if I should install a fuel pressure regulator first since the good ones run around $100 when considering hoses, etc..

Bump the timing first then turn down the idle and adjust the mix screws.
If it still smokes after that then assume it's too much fuel pressure.
Most pumps put out too much for an eddy carb.
Even edelbrock's is rated at 5.5 and no gaurentee it stays that.
Regulators can be had cheaper. No more than 50 complete. Look on summit or jeg's.

[ubtripn]

Got it, thanks!

[67 chevelle]

If you were running only on the idle circuit , your engine would shut down when the idle screws were bottomed out , your probably sucking fuel from the primary circuit . Try another carb , get someone with experience to help

[ChuckLee]

wow, that's a lot of carb there. I would put that carb on the shelf and throw a 600 or a 650 on it. that's a big part of your problem.

Also, do you know what power valve you have in the carb? If it's not correct or if it's not working correctly you could be running way more fuel than even that carb is supposed to deliver.

[ubtripn]

I am planning to downsize the carb when I have the dough. Just wanting to do what I can right now to help in any way.

I put a fuel pressure restrictor on last night, advanced my timing (we are at about 2100 feet) adjusted the idle but the air/fuel screws still need to be turned all the way down BUT I did get a huge improvement in two areas. No more black smoke except a small puff when I stand on it and a VERY noticeable increase in power across the board. It runs like a top but I know now that I am over-carbed. I wish Edlebrock still made the Rochchester (sp?) like carb. I want very small primaries. Anyway, 600 or 650 is my plan in the future.

All I did was put a $40 dollar Mr. gasket fuel pressure restrictor in line set at 5.5 but I wonder if I turned the fuel delivery down some if it would bring the idle/air screws into play. Eddlebrock says to go 6.5, it doesn't need it. I do not believe I am flooding the carb anymore and since it is running strong and the temp is dead steady maybe I should leave it alone. I don't know. But there has been improvement.

[ubtripn]

The main problem is now gone. Not turning the curb black after two minutes idling. I advanced my timing to about 22 which seems like the sweet spot to me. Took it out on a back road and it roared through the gears. No more black smoke which was my goal. I am learning alot here, thx.