72 350-4 sputter/backfire at high rpm

Discussion in 'Small Block Tech' started by 350-4lesabre, Aug 8, 2011.

  1. 350-4lesabre

    350-4lesabre Young and Dumb

    just curious how that could be if its brandnew
     
  2. 350-4lesabre

    350-4lesabre Young and Dumb

    while checking the vacum pulled the plug off the port and heard a strong hiss for about 3seconds then the engine died. could this be another problem or just too much air
     
  3. sean Buick 76

    sean Buick 76 Buick Nut

    Ok, you can rule that out then...
     
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    When you unplugged the line, you created a big vacuum leak. That leans the mixture and the engine will run rough or possibly stall. If the vacuum gauge is fluttering between 17 and 20, it could be a valve in one cylinder. Is the valve train noisy on one side?
     
  5. bhambulldog

    bhambulldog 1955 76-RoadmasterRiviera

    :) I had to ask. On a nailhead passenger front is #1:)
     
  6. 350-4lesabre

    350-4lesabre Young and Dumb

    interesting u asked that yea it is pretty noisy kinda like a steady ticking sound all the time
     
  7. sean Buick 76

    sean Buick 76 Buick Nut

    Sounds like you need to remove that valvecover and start up the engine to see what is going on... Place some old towels or something on the fender and engine bay to catch any oil that will shoot out the pushrods. You might have a broken rocker, or a bad lobe on the cam... It should only take a second to find the problem...
     
  8. 350-4lesabre

    350-4lesabre Young and Dumb

    alright cool i think ill do that today
     
  9. 350-4lesabre

    350-4lesabre Young and Dumb

    didnt have time today lol when i did go to the othere house to check on the car i forgot my keys too lol :Dou:
     
  10. 350-4lesabre

    350-4lesabre Young and Dumb

    found a reman carb (qjet) at the local parts store was wondering if that would be good for just bolting on or would it be tuned differant then a factory qjet.
     
  11. sean Buick 76

    sean Buick 76 Buick Nut

    Yeah the Reman Q jets are terrible in most cases... They build them generic and they will not be the right specs for a Buick 350. Contact Everyday Performance or Carmantx and have them build you a correct carb.
     
  12. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    No it wouldn't. Remanufactured carburetors are your WORST choice. Besides, you have no idea what is causing your problem yet.

    Read what Cliff R has to say about remanufactured Q -jets http://www.v8buick.com/showthread.php?t=231295
     
  13. 350-4lesabre

    350-4lesabre Young and Dumb

    your totally right i always jump to conclusions and over think things when it comes to my car :Dou:. is there any more info that i can give you guys that might help other than obviously pulling the valve covers.

    in the morning gonna get down to the bottom of this problem. i found a sweet deal on a set of gauges and low profile tach too that i'll be putting in hopefully i can get that done too.
     
  14. 350-4lesabre

    350-4lesabre Young and Dumb

    well found the problem. one of the rockers in cylinder 5 is only traveling about a 1/4 of what it should(if im lookin straight down its the the one on the right so idk if its intake or exhaust ", in morning gonna drain the coolant and pop the manifold off and get down to the bottom of it finally. hey u guys have been a huge help i much appreciate it.

    any more tips and advice would be cool.
     
  15. Capo

    Capo Well-Known Member

    I know this thread is kinda old now but I have the EXACT same problem, my '71 has a warn out exhaust lobe on the #5 cylinder, is that just a coincidence? Or is there something that makes that particular lobe ware out?
     
  16. 462 Chevelle

    462 Chevelle 462 chevelle

    Just coincidence. have to use zinc in oil.
     

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