black smoke at start up - The 1947 - Present Chevrolet & GMC Truck Message Board Network

57rookie · 02-15-2013, 09:20 PM

I have a very stock 86 GMC with the 305 and the 4 bbl quadrajet factory carb. It has a full tune up as I am restoring it and have put new plugs/wires,ect. on and it runs very well and idles well when warmed up but at start up it is choking its self and blowing black smoke out. I have heard that this is because my secondaries on the quadrajet are probably out of adjustment and are completely shut choking the engine of air. I don't know how to adjust this on a carburator, does anyone have tech info or pics to show me where I would adjust this. The truck runs so well once the electric choke finally seems to take hold but the black smoke and chugging at start up is very frustrating. Engine has only 60,000 original miles.
Thanks to anyone that can help.

geezer#99 · 02-15-2013, 09:52 PM

THe secondaries have nothing to do with it. You need to adjust the amount of opening the choke blade has. Yours is closed too much.
Here's a link how to adjust it open more on page 4.
http://www.vetteprojects.com/kstyer/quadrajet_4.htm

57rookie · 02-15-2013, 10:36 PM

That's fantastic. It sounds like I need to turn the screw counter clockwise. I really appreciate this. I am not even sure I have a QJet, I assumed that all GM's in this vintage do but I get I better confirm this tomorrow when I try it. I hope it does not have a Carter otherwise I will not know how to adjust.

geezer#99 · 02-15-2013, 10:46 PM

If you have a problem take a pic so it's easier for us to help. All carbs are adjustable. Each is different.

57rookie · 02-15-2013, 11:00 PM

thanks again. I will hit the garage tomorrow and see what damage I can do. It runs so smooth and strong and I did the full tune up on it last week and the carb functions very well, just loads up and floads at start up so hopefully I can adjust the plate open more to fix it. I will report back in and thank you for taking the time to help.

meatwagon83 · 02-16-2013, 12:05 AM

black is fuel your a little rich

mrolds88 · 02-16-2013, 12:34 AM

Quote:

Originally Posted by 57rookie

That's fantastic. It sounds like I need to turn the screw counter clockwise. I really appreciate this. I am not even sure I have a QJet, I assumed that all GM's in this vintage do but I get I better confirm this tomorrow when I try it. I hope it does not have a Carter otherwise I will not know how to adjust.

Not sure what screw you are talking about. What you need to do is adjust the round black piece on the passenger side front of the carb. Some of them came with the three holdowns riveted on. Thats a simple drill and tap operation. When you do get everything loose and adjustable, set it cold to about 3/16" pen. Still gives you air and pulls enough fuel when cold. Thats exactly what iI did when I had my 86.

geezer#99 · 02-16-2013, 11:22 AM

Open up the link and you'll see what screw he's talking about. If his carb has that screw then he won't need to adjust the cap.

02-15-2013, 09:20 PM	#1
57rookie Registered User Join Date: Jul 2011 Location: Calgary, Alberta Posts: 153	black smoke at start up I have a very stock 86 GMC with the 305 and the 4 bbl quadrajet factory carb. It has a full tune up as I am restoring it and have put new plugs/wires,ect. on and it runs very well and idles well when warmed up but at start up it is choking its self and blowing black smoke out. I have heard that this is because my secondaries on the quadrajet are probably out of adjustment and are completely shut choking the engine of air. I don't know how to adjust this on a carburator, does anyone have tech info or pics to show me where I would adjust this. The truck runs so well once the electric choke finally seems to take hold but the black smoke and chugging at start up is very frustrating. Engine has only 60,000 original miles. Thanks to anyone that can help.

02-15-2013, 09:52 PM	#2
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,733	Re: black smoke at start up THe secondaries have nothing to do with it. You need to adjust the amount of opening the choke blade has. Yours is closed too much. Here's a link how to adjust it open more on page 4. http://www.vetteprojects.com/kstyer/quadrajet_4.htm

02-15-2013, 10:36 PM	#3
57rookie Registered User Join Date: Jul 2011 Location: Calgary, Alberta Posts: 153	Re: black smoke at start up That's fantastic. It sounds like I need to turn the screw counter clockwise. I really appreciate this. I am not even sure I have a QJet, I assumed that all GM's in this vintage do but I get I better confirm this tomorrow when I try it. I hope it does not have a Carter otherwise I will not know how to adjust.

02-15-2013, 10:46 PM	#4
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,733	Re: black smoke at start up If you have a problem take a pic so it's easier for us to help. All carbs are adjustable. Each is different.

02-15-2013, 11:00 PM	#5
57rookie Registered User Join Date: Jul 2011 Location: Calgary, Alberta Posts: 153	Re: black smoke at start up thanks again. I will hit the garage tomorrow and see what damage I can do. It runs so smooth and strong and I did the full tune up on it last week and the carb functions very well, just loads up and floads at start up so hopefully I can adjust the plate open more to fix it. I will report back in and thank you for taking the time to help.

02-16-2013, 12:05 AM	#6
meatwagon83 Registered User Join Date: Dec 2012 Location: Preble county ohio Posts: 1,914	Re: black smoke at start up black is fuel your a little rich

02-16-2013, 11:22 AM	#8
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,733	Re: black smoke at start up Open up the link and you'll see what screw he's talking about. If his carb has that screw then he won't need to adjust the cap.



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