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Technical Stumped - Calling all Hotrodders!!

Discussion in 'Traditional Hot Rods' started by RednekYoga, Oct 6, 2019.

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  1. RednekYoga
    Joined: Feb 2, 2019
    Posts: 24

    RednekYoga

    Hey HAMB family, I'm trying to solve an issue with popping out of the exhaust when you rev motor, and some backfiring out of carb.

    My son just put a new cam and new heads on his Chevy 350 (1962 Impala). It's an Edelbrock top end kit, and all came together. When we fired it up to break in the cam, the headers got really hot and melted some plug wires and brake lines because we didn't take a minute to time it (oops!). After we put the fire out (haha what a nightmare), we re ran all the brake lines and replaced the wires and all that. We wrapped the headers, fired it up again, timed it and finished the cam break in. The motor itself never overheated at any point.

    After the breakin, we changed the oil (as was recommended), and the motor fired right up, but wer were getting popping out of both pipes when you rev it up. Also the occasional pop out of the carb too. So here's what we did:

    - replaced the cap and rotor
    - adjusted all the valves with the motor running...all are good it seems
    - reset the idle mix screws to 1 1/2 turns from bottom
    - pulled the dizzy and reset it to make sure we did it right
    - checked the plugs for fouling, they look fine

    After all that, still popping out of the exhaust and a bit from the carb. One question: could the heat from the fire fiasco have messed up the wires. There's a misfire somewhere but damned if we can figure it out.

    Any ideas out there?
    Thanks!

    RNY
     
  2. el Scotto
    Joined: Mar 3, 2004
    Posts: 4,154

    el Scotto
    Member
    from Tracy, CA

    Sounds like a leakdown test may be in order... I suspect valves...
     
    Hemi Joel likes this.
  3. fastcar1953
    Joined: Oct 23, 2009
    Posts: 1,644

    fastcar1953
    Member

    firing order set right? hei or points?
     
    loudbang and deathrowdave like this.
  4. Brand Apart
    Joined: Jan 22, 2011
    Posts: 551

    Brand Apart
    Member
    from Roswell GA

    What is base and total timing? Did you change the harmonic balancer, timing covet or timing tab. I've seen lots of guys use wrong Or mismatched components, consequentl timing is off.
     
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  5. F-ONE
    Joined: Mar 27, 2008
    Posts: 1,873

    F-ONE
    Member
    from Alabama

    Compression test is in order.
    Popping like that is a sign of a burned , open valve, stuck valve or possibly a wiped cam lobe. It could also be timing, spark and fuel.

    Do a compression test on all cylinders to rule this out. Otherwise you’ll be chasing your tail.
     
  6. Solid or hydraulic lifters? What lash settings did you use? Does the problem occur when the engine is cold or only at operating temperature? New valve springs? Are the plug wires properly separated or are they closely bundled together for any length?
     
  7. gene-koning
    Joined: Oct 28, 2016
    Posts: 1,364

    gene-koning
    Member

    Change the plug wires. You stated the fire got hot enough to melt the plug wires. If you didn't change them, do so now. If the problem is still there after the plug wires have been changes (and are in the correct position), then you need to look farther. Gene
     
    loudbang and kadillackid like this.
  8. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 297

    ekimneirbo
    Member
    from Brooks Ky

    I'd check your valve adjustment to make sure the valves actually close properly. Then I'd do a leak down or a compression test. I'm also wondering if you got the timing gear marks aligned correctly.
     
  9. deathrowdave
    Joined: May 27, 2014
    Posts: 1,776

    deathrowdave
    ALLIANCE MEMBER
    from NKy

    Valve adjustment or more than that firing order check 1st
     
  10. Tri-power37
    Joined: Feb 10, 2019
    Posts: 297

    Tri-power37
    Member

    A compression test will help diagnose a mechanical misfire like a burnt valve, flat cam lobe, bent push rod etc. etc. I bet it might be something like this with the recent top end work and getting so hot on break-in. If the compression numbers are even I would next suspect a ignition misfire.
     

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