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Need help with 85 Sierra running rough

Discussion in 'Engine & Performance' started by muddslut, Nov 19, 2020.

  1. muddslut

    muddslut Junior Member

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    Joined:
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    Location:
    Indiana
    First Name:
    Levi
    Truck Year:
    1985
    Truck Model:
    K20
    Engine Size:
    350
    I’m gonna try to get up there in the am and try that! I’ll keep everyone posted. I appreciate all the help so far!
     
  2. muddslut

    muddslut Junior Member

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    First Name:
    Levi
    Truck Year:
    1985
    Truck Model:
    K20
    Engine Size:
    350
    @Bextreme04 Okay, so I took a a little plastic test and tube tank and wire tied it up to the hood and ran it straight down into the carb. It started and idle good like it was but still the same results as before when trying to rev it up. I hooked the mechanical pump up and had the same results. I left the line that runs from the mechanical pump off after I ran it and there was plenty of pressure. I was thinking maybe put a fuel regulator on it tomorrow and see what happens? Or should I still drop the tank and check the strainer in case it still isn’t getting enough fuel when giving it throttle?
     
  3. Bextreme04

    Bextreme04 Full Access Member

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    Location:
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    First Name:
    Eric
    Truck Year:
    1980
    Truck Model:
    K25
    Engine Size:
    350-4bbl
    Maybe I’m misunderstanding what the symptoms are here. Is it starting to misfire when you rev it up? Is it running poorly after it warms up? My suggestion was to use a separate tank to the inlet of the pump to rule out the strainer. It’s unlikely that running a gravity feed directly to the carb would supply enough fuel depending on how you had it set up. A picture or video is worth a thousand words and would probably help a lot with this.
     
  4. muddslut

    muddslut Junior Member

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    Truck Year:
    1985
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    K20
    Engine Size:
    350
    @Bextreme04 if I ease into it it will rev up until about to where it’s WOT and it starts to cut out. If I gas it really quick at an idle it will cut out then backfire out of the carb and either struggles to catch up with itself or it dies. If I go down the road it runs good for about a block or two and then I start having the same symptoms. After it dies going down the road it takes a little encouragement to start. Once it starts I practically can’t give it any gas cause it will almost instantly die, until it sits for 5-10 minutes then it’ll do it all over again. I’m sorry if I’m not clear on some things I’m trying my best. As far as the test and tune tank I was using I just had the container wire tied up to the open hood, and then ran the hose from the petcock on the tank down into the carb inlet, not literally straight down into the carb if that’s what you thought I meant.
     
  5. Bextreme04

    Bextreme04 Full Access Member

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    Truck Year:
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    Truck Model:
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    Engine Size:
    350-4bbl
    hmmm, that sounds like either you have it going really rich, you have a timing issue, or there is something mechanically wrong with the engine. You should mechanically verify TDC on #1 and make sure the distributor is on #1 when you are on the compression stroke. I’d also run a compression test to see if any of the cylinders were weak. You could have a worn cam live or other valve train issue. I had a similar issue that just happened out of the blue and it turned out to be a broken valve spring.
     
  6. Jonny B

    Jonny B Junior Member

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    Location:
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    First Name:
    jon
    Truck Year:
    1974
    Truck Model:
    gmc c1500
    Engine Size:
    350
    lots of good replies,if carbs fine on camaro then thats ticked,undo fuel line befor carb/after pump and pump fuel through into container.connect mechanical fuel pump to spare fuel can putting hose into fuel can and run engine at various rpm and see if there is a result.Timing needs setting but prob not the cause here.Yes defo check compression on each cylinder and check plugs colour.Good fuel?good fuel filters?etc,etc.step by step check and eliminate.Does radiator lose coolant and is engine temp ok?If head gasket is leaking it will run like crap
     

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