Welcome to Club Hot Rod!  The premier site for everything to do with Hot Rod, Customs, Low Riders, Rat Rods, and more. 

  •  » Members from all over the US and the world!
  •  » Help from all over the world for your questions
  •  » Build logs for you and all members
  •  » Blogs
  •  » Image Gallery
  •  » Many thousands of members and hundreds of thousands of posts! 

YES! I want to register an account for free right now!  p.s.: For registered members this ad will NOT show

 

Thread: 350 Chevy-carb Backfire
          
   
   

Reply To Thread
Results 1 to 12 of 12
  1. #1
    Mr Blue's Avatar
    Mr Blue is offline CHR Member Visit my Photo Gallery
    Join Date
    Nov 2007
    Location
    Bonita Springs
    Car Year, Make, Model: 23 Ford T, 2004 ZO6 Vette, 99 Mustang
    Posts
    541

    350 Chevy-carb Backfire

     



    Hello all,
    Need some expert advice. The 350 chevy engine with a quadrajet carb in my boat is experiencing a strange problem. It only happens above 1900 RPMS.

    It backfires through the carb. It will idle all day long up to about 1800-1900 RPMs but then when you put a load on it the problem starts. We took it out last weekend with no issues, but then it did it again yesterday. All standard parts are new (plugs, wires, cap, rotor) rebuilt carb. It never fully shuts the engine off, it just starts cutting out until I bring it down to idle and then it is fine there

    One side note. the crossover passages on the intake manifold that feeds warm air to the carb base have turned white on both sides of the carb.

    Any advice would be much appreciated! thank you, Don
    Don Jr.
    "Once again I have thoroughly disgusted myself"

  2. #2
    jerry clayton's Avatar
    jerry clayton is offline CHR Member Visit my Photo Gallery
    Join Date
    Feb 2006
    Location
    Bartlett
    Posts
    6,831

    did you just put this carb on with the plugs, wires????

    It is super lean but the fix/cause depends on what type carb---you didn't put a Holley on an quad jet manifold???

  3. #3
    Mr Blue's Avatar
    Mr Blue is offline CHR Member Visit my Photo Gallery
    Join Date
    Nov 2007
    Location
    Bonita Springs
    Car Year, Make, Model: 23 Ford T, 2004 ZO6 Vette, 99 Mustang
    Posts
    541

    Thank you for the reply.

    It is a quadrajet cast iron GM manifold. (no adapters)

    I did rebuild the quadrajet along with putting the plugs, wires, etc. on at the same time.

    Thanks again for the assistance! Don Jr.
    Don Jr.
    "Once again I have thoroughly disgusted myself"

  4. #4
    ted dehaan's Avatar
    ted dehaan is offline CHR Member Visit my Photo Gallery
    Join Date
    May 2003
    Location
    whittier ca.
    Car Year, Make, Model: 32ford5w,60fordstarliner,55chevy65corvai
    Posts
    645

    I hope I'm wrong but if you hold the throttle at a steady rpm of about 2000 to 2300 and it pops through the carb that is a classic symptom of a flat cam like I said hope I'm wrong and its just a tune up problem good luck.....ted
    I'LL KEEP MY PROPERTY, MY MONEY, MY FREEDOM, AND MY GUNS, AND YOU CAN KEEP THE CHANGE------ THE PROBLEM WITH LIBERALISM IS SOONER OR LATER YOU RUN OUT OF OTHER PEOPLES MONEY margaret thacher 1984

  5. #5
    Mr Blue's Avatar
    Mr Blue is offline CHR Member Visit my Photo Gallery
    Join Date
    Nov 2007
    Location
    Bonita Springs
    Car Year, Make, Model: 23 Ford T, 2004 ZO6 Vette, 99 Mustang
    Posts
    541

    Hey Ted,
    Thank you. Yes I hope it is not a cam lobe to be sure. I do not think it is as the problem has been intermitent.

    A flat cam lobe would create a problem at all rpms and it runs like a champ and idles perfect.
    Don Jr.
    "Once again I have thoroughly disgusted myself"

  6. #6
    jerry clayton's Avatar
    jerry clayton is offline CHR Member Visit my Photo Gallery
    Join Date
    Feb 2006
    Location
    Bartlett
    Posts
    6,831

    Are the metering rods stuck shut, or partially shut?

  7. #7
    Mr Blue's Avatar
    Mr Blue is offline CHR Member Visit my Photo Gallery
    Join Date
    Nov 2007
    Location
    Bonita Springs
    Car Year, Make, Model: 23 Ford T, 2004 ZO6 Vette, 99 Mustang
    Posts
    541

    Going to check all of the basics this weekend. My schedule (and the marinas hours. she is in dry storage inside) prevents me from getting to her to check the basics. Will look into all aspects of the carbs operation as well as plugs condition etc. I just dont feel like this is a major engine issue as the boat runs great most of the time. I feel i have a lean condition perhaps. Thoughts?
    Don Jr.
    "Once again I have thoroughly disgusted myself"

  8. #8
    HOSS429's Avatar
    HOSS429 is offline CHR Member Visit my Photo Gallery
    Join Date
    Jun 2007
    Location
    New Market
    Posts
    2,584

    were you trying to fix an old problem or did you create this problem with your tune up ?
    iv`e used up all my sick days at work .. can i call in dead ?

  9. #9
    Mr Blue's Avatar
    Mr Blue is offline CHR Member Visit my Photo Gallery
    Join Date
    Nov 2007
    Location
    Bonita Springs
    Car Year, Make, Model: 23 Ford T, 2004 ZO6 Vette, 99 Mustang
    Posts
    541

    This was a freshening up of the engine that was in there already. After the tune up we had 6-7 no problem trips. This problem surfaced after she had been running fine for a while and even then it does not occur every time. In fact the engine ran perfect all the way to our destination that day (about an hour run) and then started the problem on the way back (about 3/4 of the way back) so strange. Thanks for any input. Don Jr
    Don Jr.
    "Once again I have thoroughly disgusted myself"

  10. #10
    Mr Blue's Avatar
    Mr Blue is offline CHR Member Visit my Photo Gallery
    Join Date
    Nov 2007
    Location
    Bonita Springs
    Car Year, Make, Model: 23 Ford T, 2004 ZO6 Vette, 99 Mustang
    Posts
    541

    Ok,
    Finally got to work on that backfire issue this weekend.

    Heres what I found.

    Timing was way off. my marine manual for that boat recommends 4 degrees BTDC. My timing was set at 6 degrees ATDC (way off) I had a very hard time getting the engine timed as the harmonic balancer is sitting almost directly against the boats front bulk head (in other words I was bent like a pretzel trying to get to the timing marks with the timing light)

    I adjusted the air/ fuel mixture on the quadrajet also (bottomed them out gently and backed out 3 turns each)

    Accelerator pump arm has two settings. This enging was on the farthest out hole, the good running engine was on the inside hole. Changed the location.

    My thoughts of this engine running lean were not true. All of the plugs showed that the engine was running rich,not lean. Cleaned them, regapped and installed.

    Checked all spark plug wires to be safe that they were not crossing eachother for a chance of a crossfire between cylinders.

    Test ran the engine on land (on the garden hose) ran great. Went to go out Sunday after working on it all day Sunday..........AND IT RAINED!! So I will have to wait to see if it cured my issues under load. We shall see. Any thoughts from my diagnosis? Thanks to all. don Jr.
    Don Jr.
    "Once again I have thoroughly disgusted myself"

  11. #11
    jerry clayton's Avatar
    jerry clayton is offline CHR Member Visit my Photo Gallery
    Join Date
    Feb 2006
    Location
    Bartlett
    Posts
    6,831

    Rained???? Snowed up here

  12. #12
    Mr Blue's Avatar
    Mr Blue is offline CHR Member Visit my Photo Gallery
    Join Date
    Nov 2007
    Location
    Bonita Springs
    Car Year, Make, Model: 23 Ford T, 2004 ZO6 Vette, 99 Mustang
    Posts
    541

    Now I don't feel so bad.......I will take rain over snow any day of the week. (and it was in the low 80's too!)

    Next trip out will be Easter Sunday (weather permitting) We shall see if we cured the problem!

    Don Jr.
    Don Jr.
    "Once again I have thoroughly disgusted myself"

Reply To Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
Links monetized by VigLink