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Stoevebolt Backfires Through Carb

Discussion in 'The Hokey Ass Message Board' started by curtisgreenjeans, Nov 24, 2013.

  1. curtisgreenjeans
    Joined: Jul 30, 2013
    Posts: 13


    <style> <!-- /* Font Definitions */ @font-face {font-family:Calibri; panose-1:2 15 5 2 2 2 4 3 2 4; mso-font-charset:0; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:3 0 0 0 1 0;} @font-face {font-family:Cambria; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:3 0 0 0 1 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:Cambria; mso-fareast-theme-font:minor-latin; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} /* List Definitions */ @list l0 {mso-list-id:869341257; mso-list-template-ids:883212684;} ol {margin-bottom:0in;} ul {margin-bottom:0in;} --> </style> I bought a '51 Chevy back in July with a rebuilt 235. The car ran great, but the old PowerGlide transmission was leaving a trail of fluid everywhere we went. After spending a chunk of cash to rebuild the transmission, I took the car on a 200-mile excursion to the Old Geezers Show in Lamar, MO.

    On the return trip, within a block of my house, the car died in the middle of the street. After enduring lots of dirty looks from people, it fired back up, but the motor has run like crap since.

    The initial theory was that I'd ran the tank low on fuel and sucked a bunch of crap up into the carb. So,
    I rebuilt the Carter YF a few weeks back, eliminated the sediment bowl and put a fuel filter in its place.

    I got the motor running pretty good at idle. However, under a load, it backfires through the carb frequently (usually killing the car). I’ve double checked my work on the carb and everything seems to be working correctly and the float is set to the specifications outlined in the kit.

    There are lots of theories, but it seems like most people agree it MIGHT be a couple of things:

    • There’s a vacuum leak somewhere
    • Timing is off

    Any suggestions or additional theories would be much appreciated. And before I screw anything up too bad, if there's anyone who can suggest a shop around Springfield, MO that would be willing to work on the car that would also be helpful.

  2. If you have ruled out the carburetor then it sounds like an ignition problem to me. I have seen a carbon tracked or cracked cap act like that. Check all of you ignition components including plugs,points, condenser and wires. I'm assuming you already checked timing. Could also be a tight intake valve.
  3. bobwop
    Joined: Jan 13, 2008
    Posts: 6,086


    short of fuel

    have you pulled the fuel line at the tank? I bet there is an obstruction of crud.
  4. How is the valve adjustment?
    Had a car once that was running great but after a few miles had a small backfire through the carb. While trying to figure out what it was the prob kept getting worse and backfire was really loud. Checked carb and intake. Nothing.
    Removed valve covers to Inspect and found one exhaust rocker had fallen off of valve. This caused the exhaust to pushed back through carb. Just a thought
    Maybe your valves are not fully opening after the long trip.
    Those tappets get beat after long hard trips

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  5. squirrel
    Joined: Sep 23, 2004
    Posts: 46,135


    Lean mixture, late or weak spark, or a valve not closing or opening will cause similar backfiring thru carb symptoms.

    If it had old gas in it, and you drove it around, it's possible it stuck some valves, and possibly bent a pushrod or two.
  6. carbking
    Joined: Dec 20, 2008
    Posts: 2,797


    A backfire through the carburetor is caused when there is pressure in a cylinder when an intake valve is open.

    Probable percentages:

    (1) ignition - 95 percent
    (2) valve issue (sticking, burned, timing gear, etc.) - 4 percent
    (3) everything else - 1 percent

    Pretty easy to eliminate either a burned or sticky valve with a compression test. Pretty easy to test the ignition system with a diagnostic oscilloscope.

  7. thru the carb- seeking fuel,,,thru exhaust- seeking air
  8. midnight auto parts
    Joined: Feb 1, 2007
    Posts: 59

    midnight auto parts
    from tn

    it,s hungry--check the rubber lines under the car for cracks, maybe sucking air instead of fuel
  9. That's my kinda post right there !
  10. anthony myrick
    Joined: Sep 4, 2009
    Posts: 5,830

    anthony myrick

    my 235 was running fine then started backfiring (exhaust) and spitting back thru the carb. Did like you and cleaned up the carb, still done the same, replaced points and ran better for a little while then back to running rough. Called my old mechanic friend, he said to check the ballast resistor next, he was correct it had corroded and was burning up the points causing the backfire condition. maybe this can help you.
  11. Pete Eastwood
    Joined: Jul 27, 2011
    Posts: 913

    Pete Eastwood
    from california

    90% of all carburetor problems are electrical !
    check the condensor !
  12. Check your ignition. Start with the condenser, then the points, and then the coil. It's one of the three.

    A weak spark or an electrical issue will give you symptoms that you'll swear is fuel related. We tend to look at the fuel system first, but you have to remember that you've got to have spark for the fuel system to do it's job.

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