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Loss of power at around 15-35mph

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by chevblazk5, Jul 28, 2003.

  1. chevblazk5

    chevblazk5 1/2 ton status Premium Member

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    The truck is a 1980 Chevy K20 with 350, Edelbrock intake, Edelbrock carb and here's my problem. The truck starts fine cold or hot, but she starts bogging at around 15mph to 35mph. (Loss of power comes first and then the bogging.)
    I started having this problem a month ago when I still had The Holley truck avenger carb, but I was having many different problems with this carb from day one, so I went out and got an Edelbrock performer. The problem went away for about 3 days but just like a bad cold, it came back. So, I got a new fuel pump, fuel lines, fuel tanks, wires, plugs and distributor. I changed the intake gasket and I triple checked the timing. There are days when the truck runs like a clock and there are days when I can't drive it out of the driveway because of this. I had to have the truck towed from the office parking lot last week because I couldn't drive it. The shop had the truck for a week, drove it for 120 miles, and couldn't find anything wrong with it. This is driving me nuts and before I drive it of the cliff can anybody give me any ideas of what I should check/fix?
     
  2. Confedneck

    Confedneck 3/4 ton status

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    how nasty is the carbon build up? fuel filter? if a shop had it for 120 miles and couldnt get it to act up..does it do it after it came out of the shop??is is possible you have a loose adjustment screw somewhere? maybe a loose dist. hold down that allows timing or fuel trims to change under bad vibrations??
     
  3. chevblazk5

    chevblazk5 1/2 ton status Premium Member

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    What or where would I check for carbon build up? I changed the fuel filter when I changed the fuel pump last Satudrday. I got the truck back Friday and I drove it around for about 60 miles without a problem. Saturday morning on my way to work it started acting up again. Later that day I changed the fuel pump, plugs, wires and distributor. (I changed the fuel tanks and all new lines three weeks ago.) I checked every nut and bolt under the hood and I think that the only loose screw is up in my head /forums/images/graemlins/cool.gif
    Two things I forgot. One, the motor is two years old with 23,000 miles. PO worked at the chevy dealer and had a crate motor installed. Two, just before she starts acting up, I feel slight vibrations. I can't tell where the vibrations are coming from, but it almost feels like they're coming from the transmission.
     
  4. ramjet gmc

    ramjet gmc CK5 Staff Staff Member Moderator GMOTM Winner

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    i am thiking cloged cat anyone want to take a stab
     
  5. chevblazk5

    chevblazk5 1/2 ton status Premium Member

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    I got no cats
     
  6. prjt_blzr

    prjt_blzr 1/2 ton status

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    I have seen intermittent ignition modules with this type of behavour. It starts to drop spark and the engine runs like crap. Pretty bizarre because they will run and idle fine, just won't make power. It is a $20 part that you should have a spare of anyway.
    Good Luck,

    Mike
     
  7. Thunder

    Thunder 3/4 ton status

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    Sounds like iginiton problem to me too. Replace the dist module.
     
  8. chevblazk5

    chevblazk5 1/2 ton status Premium Member

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    I replaced the dist module, wires and plugs this morning. While I was changing the wires I noticed that the vacum line from carb to trans was disconected. I set the timing and drove it for about 80 miles without a problem so it seems like you guys were right /forums/images/graemlins/thumb.gif
     

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