78 2bbl idle and choke acting up

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BRN78BLAZER, Apr 21, 2003.


    BRN78BLAZER 1/2 ton status

    Feb 5, 2003
    Likes Received:
    Stoney Creek Ontario, Canada
    I couldn't find any 2 bbl info using a search, so here's the problem. It's a rebuilt 2 barrel rochestor on the origional 305 in my 78. The origional carb was great, it started great, ran great, but a year ago was replaced cause the vehicle was hesitating and sometimes stalling. When we put the new carb on it did the same thing and we thought to check the new filter, and found that it had come apart and a device which is supposed to block the back flow when it is shut off, was actually blocking the flow when it was running.

    Now the old carb being long gone we did our best to set this one up as best we could, but it was never right. It would always have a lumpy idle when you started after it had been sitting during the day.

    The vehicle sat from last may till early september without running once, and when I started driving it again it was fine. It would start without the choke coming on idle around 700 and once it warmed up would idle more like around 800. When the cold wheather came the fast idle and choke came on and would stay on for about half a mile, then it would idle at 700, then at 800 when warmer. This seemed perfect to me, and I never touched it cause it was running so good.

    Heres where the problems start. About a month ago, as I would be going along turning say 1500, as you came up to a stop the idle would stay up around 1500. I thought it was the fast idle so I cleaned all linkages making sure everything was free. A week later it was doing it again. I poped the hood to look at the fast idle came and noticed it was on the low step. I put a stronger throttle spring on and this seems to have fixed that problem, but I don't think I should need such a strong spring. With the cable disconnected I can move the throttle very easily and it dosen't stick or bind at all.

    A week later and the fast idle is staying on way to long, and this is warm wheather when it shouldn't be on at all. It was staying on about 2 miles. So I back off the choke, but now it won't idle when you first start it. You have to do it with the pedal for a min, then the fast idle comes on and still stays on for over 1 mile. Back it off more and you have to keep it idleing with the peadal even longer and fast idle stays on for the same amount of time, over one mile.

    What is going on with this thing??? I've checked everything as in plugs wires, vacumm, timming. There is nno egr, or cat on this, only a pcv, and someother device run by vacumm that has something to do with the idle but I don't know what. It's like a little plunger that a/c vehicles have, but it was there before I put the a/c in. The choke operated by a rod that comes from a coil mounted down on the intake manifold.

    Can anybody help me??? This is so frustrating and I need help asap. Sorry for the long post, I just wanted to describe every little detail as it may make a difference.

    Thanks to all who can help
  2. azblazor

    azblazor 1/2 ton status Premium Member

    May 5, 2001
    Likes Received:
    Arizona, Phoenix area
    Wow, good detail, I don't do carbs anymore ( never did them well). But if you can get Grim-Reapers attention ( or maybe PM him) he seems to know carbs real well. Bump to the top.
    Good luck.

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