Runs rough first few minutes

[Rc 415]

Hey guys, I am having some trouble with my 83 stepside running rough for the first few minutes after starting it up, and I need some help. Ok, first off this only happens if I havent started the truck for a day or so. So when I start the truck after its been sitting, it expells a fair ammount of black smoke out of the tailpipes for a few minutes, and its kinda jumpy as if its about to die or somthing. then after the black smoke stops, there is a gray smoke that dissapates very quickly that comes out the tailpipes for a few minutes until the truck warms up, I think thats normal though. There was one day that I hadnt started the truck for 2 days, and when I did start it it was very rough and a lot of black smoke and it died shortly after starting, but I was able to start it back up without any problems and it did the black smoke for a few more minutes and then it got better like always. I am thinking that this involves the carberautor and or choke, can anyone give me any help on what I should do to fix the problem?

[HuggerCST]

I would start by checking the choke pulloff. The diaphram inside has probably gone bad, and is not pulling the choke open after startup, causing a rich condition, and the black smoke. Is this a 4bbl Quadrajet? If so, the pulloff is the small (half dollar size) round thing mounted on the right front of the carb. Vacuum supplied by the rubber hose on the front pulls the choke open slightly untill the engine warms up.

[Rc 415]

It is a Rochester 4 Bbl quadrajet, I will check the choke tomorrow, thanks for the insight!

[HuggerCST]

Thank you for thoroughly explaining the symptoms. It's not often that a mechanic gets that! I hope you figure it out, but if you need anymore help let us know.

[Rc 415]

Here are a few pics, how can I check if the choke pulloff is bad?

[HuggerCST]

OK, lets see if I can make sense here. You could check it several ways, but, with the engine running, the pulloff will pull in the linkage on the top left (from this view) in until the choke flap opens about 1/8th inch or so.
Or, without it running, Push the linkage(the part with the screw & spring on the end) into the pulloff canister and hold it. Take a pair of pliers and squeeze the vacuum hose closed, and hold it. Now let go of the linkage. If the vacuum holds the linkage in, it's good. If it comes back out, it's bad. I'm not good at explaining things like this, so I hope that made sense.

[Rc 415]

That makes perfect sense, thanks I'll give it a shot tomorrow!

[Rc 415]

it is indeed the choke pulloff I'm going to pick up a new one tomorrow at Napa.

[HuggerCST]

Cool. I'm glad it's a simple fix for you.