Crappy running 85 GMC.

Discussion in 'Engine & Performance' started by Irishman999, Jan 17, 2011.

  1. Irishman999

    Irishman999 Full Access Member

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    When the truck is cold it runs fine, after its been at operating temp for a while I get bad hesitation. Right off the line it tries to die out, while driving if I try to accelerate it dogs out for a second and then goes. This sounds like the plunger in my carb, I just don't understand why this would be a thermal issue.

    My transmission I just put in is now making the same weird grinding sound the last one started to make a couple thousand miles before it went bad. IM SO TIRED OF BUYING PARTS!
     
  2. HotRodPC

    HotRodPC Administrator Staff Member

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    Are you sure you have plenty of gear oil in the trans this time? Are you sure you're not losing your gear oil the Tcase adapter? Or is there a problem with the Tcase that is causing the rear bushing to go out in the transmisision maybe? Gotta consider all things. Those are just some guesses, since I can't hear or inspect it.

    As far as a used engine if you find one, don't be afraid to compression test it before you buy it. Even if you hear it run, I'd recommend a compression test. Also, take you a manual oil pressure guage and start it up. If oil pressure is good, then thats a sign the bearings are in good shape. So, oil pressure can tell you condition of the bottom end, compression test can tell the condition of the top end. Keep in mind, if its only got 30 psi oil pressure cold, its likley to only have 20 after its warmed up and I wouldn't call that good. I'd want to be seeing 40-50 cold.
     
  3. Irishman999

    Irishman999 Full Access Member

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    Transmission is full of oil, no leaks. The input shaft bearing is gone and I did not catch it while I was putting it in, everything seemed fine so I changed the front seal and stabbed her! I figured the bearing would last, I have done it before but it just started grinding like maybe the bearing is giving a-lot more tolerance than its supposed to.

    I might adjust my plunger linkage and go from there, if my 305 was losing compression it should smoke when its warmed up right?
     
  4. HotRodPC

    HotRodPC Administrator Staff Member

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    That noisy bearing can go another 100,000 miles before it comes apart. Its just noise.
    That plunger you keep calling a plunger is the accelerator pump abbreviated acc pump or ass pump if you want. I wouldn't expect anything from adjusting it.
    If its not working, its not working. Adjusting it is not going to make the rubber work any better. You got another old Qjet laying around? Just rob the accelerator pump from it if its known good.
     
  5. Old77

    Old77 Super Moderator Staff Member

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    You just said "ass pump" and "rubber" in the same post..... looking.gif
     
  6. Swims350

    Swims350 Full Access Member

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    ok pull that new clear dist. and send it this way then.
     
  7. Old77

    Old77 Super Moderator Staff Member

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    :nono: you may have to fight hrpc for that thing! :D
     
  8. Irishman999

    Irishman999 Full Access Member

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    Right now I am running the AFB, I know on the qjet you could adjust the lever that pushes the accelerator pump depending on what application the carb is on. I cant remember if thats the case on the Carter AFB. I guess the next step would be to throw a rebuild kit on it and see if that fixes the problem.

    How likely is it that there is a vacuum leak through the valve guides?
     
  9. Swims350

    Swims350 Full Access Member

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    could be put a vac. gauge on it. I have a guide for them saved and if it jumps wildly it's a sign of worn valve guides. I don't think you need a kit, but it may not hurt if it's not a fresh rebuild, I was thinking you may need to adjust the needles or springs in the top of it.

    Have you tuned the carb mixture screws with a vac. gauge? if not definately need to, it may just be lean and the mixture screws fix it. They say if you screw them all the way in and they do not bog it down or kill it out the jets are too big.
     
  10. Irishman999

    Irishman999 Full Access Member

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    I think I saved the same chart but I cant find it now! if you can find it please feel free to post it up. My next move is getting a vacuum gauge, I should have done that in the first place haha.
     
    Last edited: Jan 18, 2011
  11. Old77

    Old77 Super Moderator Staff Member

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    Post that chart up. Could be useful to others as well:)
     
  12. HotRodPC

    HotRodPC Administrator Staff Member

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    You also may not even need a kit. If you can carefully pull the top off the carb and inspect it for dirt, it might just need to be cleaned out a bit. Are you using a good fuel filter on it? One little piece of debris get into a idle circuit and it will run like crap. Also, what kind of choke does this carb have? Is the choke working? This might be why its a thermal problem. With choke on you don't notice the problem so much, but as the choke comes off the problem becomes prominant.
     
  13. Irishman999

    Irishman999 Full Access Member

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    I just took my wife to school with it, the air was decently cool out this morning and it ran just fine. I think your choke theory is right, its an electric choke and it is working. Its got an inline filter on the line and I am thinking another one inside the carb, but I never checked.
     
  14. HotRodPC

    HotRodPC Administrator Staff Member

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    Then that would tell me the problem is Carb related. As long as the choke is on, its running OK, but choke comes off and allowing the carb to meter fuel all on its own, then it tends to go down hill when the choke comes off. The choke being on is just masking the problem. Prolly time to clean out the carb, and as you mentioned, it does sound like its in need of an accelerator pump. Of course an accelerator pump will likely not ever leave you stranded, you'd just have to do slow gradual take offs. Accelerator pump just gives a quick shot of gas to get started when you first hit the gas, after that its not functional.
     
  15. Irishman999

    Irishman999 Full Access Member

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    One of these days I might have a good working carb..... This just means dont always trust a mans word on craigslist.

    I had a leaking power steering pump last summer, Put one on and now my steering box is leaking like a siv! Damn it! It never ends with this thing.
     

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