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Technical 350 chevy with issue

Discussion in 'The Hokey Ass Message Board' started by 55 dude, Jun 21, 2014.

  1. hope this isn't to off topic but my hauler a 78 C20 isn't running right. this developed back in october coming to washington from socal. i rebuilt Qjet no change, did complete tune up with 8mm wires and HEI cap has brass terminals (made in canada) no change. here is video i did today with my phone. as you can see it idles great. i'm leaning towards cam issue. thanks!
     
  2. dave lewis
    Joined: Dec 12, 2006
    Posts: 1,378

    dave lewis
    Member
    from Nampa ID

    Flat cam.
    If there is no valve train noise, pull the valve covers and do a thorough inspection.
    Dave
     
  3. thats what i was thinking. thanks! anyone else?:eek:
     
  4. A tune up and carb rebuild wont fix that racket :)
    Sounds tinny on my end

    A vacuum gauge can show you a flat cam
    A compression test will to and a dynamic compression test definitely will.
     

  5. Grahamsc
    Joined: May 13, 2014
    Posts: 466

    Grahamsc
    Member
    from Colorado

    The audio on my I phone isn't that good but if its popping back through the intake it is usually an exhaust lobe worn flat.
    The exhaust gasses have no where to go and push back through the intake valve.
     
  6. my next step! thanks for the input!:cool:
     
  7. inthweedz
    Joined: Mar 29, 2011
    Posts: 580

    inthweedz
    Member

    Double valve springs??? maybe is 1 broken, (had that on my 350, idled great, but not enough pressure to close the valve above idle) or maybe pulled the bottom out of a rocker..
     
  8. stimpy
    Joined: Apr 16, 2006
    Posts: 3,546

    stimpy

    sounded like my K 30 CS when it did it ( about 75K miles ) started bucking a little on the highway in the Pa mountains under load . at idle you could see the carb back spit or fog if you unplugged the cylinder

    if the timing chain cover never has been removed its more than likely a flat cam as that was the years of the recall for it ( up to 1980 ) verify with vac gauge like said, also check, and pull the rocker covers and use the timing light method for checking lift it will show up like a sore thumb .

    the recall repayment ended about 1990 as mine went in 87 , great time to replace to a better cam as the factory cam ( car cam ) was garbage for towing or milage with any gear higher than 3:55 ( I had 4:56 on a 16.5 )
     
  9. thats what it was doing loaded through the mountains bucking a lot! hope this thread helps someone else!
     
  10. jetnow1
    Joined: Jan 30, 2008
    Posts: 2,152

    jetnow1
    ALLIANCE MEMBER
    from CT
    1. A-D Truckers

    Also check your heads for cracks those were some of the most frequently cracked heads
    stock.
     
  11. txturbo
    Joined: Oct 23, 2009
    Posts: 1,771

    txturbo
    Member

  12. stimpy
    Joined: Apr 16, 2006
    Posts: 3,546

    stimpy

    if you find the offending cylinder and need the truck you can pull the plug wire or zerogap the plug ( which is better for the hei ) and drive it for a little bit ( about a week ) but try not to put a load on it as the uneven heating of the head can screw it up .
     
  13. Commish
    Joined: Jan 9, 2010
    Posts: 379

    Commish
    Member
    from NW Ok

    Little hard to tell in the video, but if it seems to be coming back through the carb, then I am going with the consensus, cam going flat. Intake lobe, exhaust won't do that. But pull valve covers first, could be a rocker off, or a push rod punched through if it has a lot of miles.
     
  14. guys i appreciate all the feedback!
     
  15. Fuck it - just run it. It's only got to make 16 hrs then it can die
     

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