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Carb backfire?..

Discussion in 'Early CJ5 and CJ6 Tech' started by Angel, Feb 26, 2016.

  1. Feb 26, 2016
    Angel

    Angel New Member

    New Salem, NC
    Joined:
    Feb 10, 2016
    Messages:
    16
    I am at a loss here. Dunno what else to do. I took the one change at a time approach.

    I've replaced the prestolite distributor with a delco. Verified correct parts using service manual and this site.
    Replaced plug wires. New plugs Sept 2015, cleaned up, read fine.
    Tested ignition coil, passed, did not replace.
    Rebuilt the carb using info from post here. Getting two even streams. I can't thank you guys enough!
    Found a small intake leak, fixed it with new feel pro gaskets.

    All this leads to no change. Sputters, backfires in carb at wide open throttle. Exhaust is not clogged.

    All the work was worth it. It runs so much better now, but still have the WOT issues. It will idle uphill on first gear. Give it gas, no hesitation. It would hesitate before...

    I timed it at 5 degrees, dwell set at 30, idle at 700 rpm, intake measures 20@ idle. Starts easy, it needed the maintenance.

    I even tried to rev it up while trying to change the timing with the other hand, thinking my timing marks are off.

    I noticed the dwell meter never went above 8 volts while revving.... Also on the firewall, how do you test the resistor? Can my stock Motorola alternator be the cause?

    It has plenty of power, this is just on WOT. It don't overheat.

    Thanks for your input,

    69 stock dauntless
     
  2. Feb 26, 2016
    WadeS

    WadeS Member

    Joined:
    Nov 7, 2013
    Messages:
    96
    Huh.
    My 66 v6 has run great for all the time I've owned it 2 years. I tried to adjust the choke a little. ( installed a new cable) . So I adjusted the idle just a little. Boom. Starts backfiring and running rich. I feel your pain brother man. W
    We need some help.
     
  3. Feb 26, 2016
    WadeS

    WadeS Member

    Joined:
    Nov 7, 2013
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    96
    I've heard those coil resistors can cause problems. Mines only a few months old
    but hey.... Maybe.
     
  4. Feb 27, 2016
    Tom_Hartz

    Tom_Hartz Member 2020 Sponsor 2019 Sponsor

    North Carolina
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    Apr 9, 2014
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    374
    I have found that ballast resistors work or don't work. I have also had a bad coil before and that made the engine backfire.
     
  5. Feb 27, 2016
    scoutpilot

    scoutpilot Member 2019 Sponsor

    Asheboro, NC
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    Jun 7, 2014
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    274
    Are you certain the timing advance mechanism is working correctly? No cracks in the distributor cap? How old is the fuel?
     
  6. Feb 27, 2016
    homersdog

    homersdog Tulsa, Ok 2020 Sponsor 2019 Sponsor

    Tulsa, OK
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    Jan 8, 2012
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    My first thought was also a hairline crack in the distributor cap. You are in a humid area of the country, so this would be more relevant.
     
  7. Feb 27, 2016
    Angel

    Angel New Member

    New Salem, NC
    Joined:
    Feb 10, 2016
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    16
    It ran ok last year. Enough to hit 75 mph easy. It had a miss and idled rough. I had the prestolite in it before so I thought I needed points, cap and a condenser. The vacuum advance was not working so I bought a new delco distributor with all new parts. I also decided to get new wires. Changed distributor, same then did wires, same problem still there. I then rebuilt the carb, it needed to get done bad... glad I did it. This fixed the idle to silky smooth and no hesitation. I then found an intake air leak. Oil was coming up the studs and a small leak front and rear of the intake. Glad that's done too. All the work made it idle and run better, except under load. I double triple quadruple checked timing, dwell, timing advance, I have it down to an art now.

    I have not changed the coil... I plan on picking one up next.
     
  8. Feb 27, 2016
    Angel

    Angel New Member

    New Salem, NC
    Joined:
    Feb 10, 2016
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    Has anyone noticed that the resistors for prestolite and delco have different part numbers? I'm going to pick up the bwd delco resistor and a new coil.... maybe that will fix it! One change at a time......
     
  9. Feb 27, 2016
    PeteL

    PeteL Member 2020 Sponsor 2019 Sponsor

    Hills of NH
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    Aug 3, 2003
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    Just possibly sticky valves. Seems to be more frequent with modern fuels.
     
  10. Feb 27, 2016
    Angel

    Angel New Member

    New Salem, NC
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    Feb 10, 2016
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    I think you may be right on the sticky valves! I replaced one at a time, resistor and coil, no change. Meausred old accell 8140 coil next to new one. Same measurements. Measures old prestilite resistor @1.2 ohms vs the specified delco @2.1 ohms. Still no change. I did notice that my alternator wasn't charging again... a few bangs on top and it started charging @ 13.95 volts. I picked up a 76 skylark 10si rated @63amps for an upgrade. I dont think this will affect anything. Looks like worst case scenario is sticky valves or worn lobes. Thoughts?

    With any change i bring it to operating temperature and tripple check dwell, timing rpms, and air guage on manifold. Looks like it's time for a rebuild. Maybe try another condenser....idk at this time...at a loss... thoughts?
     
  11. Feb 28, 2016
    PeteL

    PeteL Member 2020 Sponsor 2019 Sponsor

    Hills of NH
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    Before a rebuild, to lube the valve stems you could try adding some MMO, ATF, or other "upper end" additive to your fuel, run a tankful and see if it helps. Enough to make smoke seems to be the consensus - some old car guys pour it right down the carb.
     
  12. Feb 28, 2016
    Angel

    Angel New Member

    New Salem, NC
    Joined:
    Feb 10, 2016
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    Tried pouring MMO down the carb with choke slightly pulled to keep the rpms up. Got some nice white smoke. No change. Replaced the motorla alternator with a delco 10si. Running good voltage 14.75. No change. Pulled all plugs. They all show the same. Running hot, lean or sticking valves. I'll buy new plugs and see what the new ones read. Old plugs are autolite 85. Going platinum. ...
     
  13. Feb 29, 2016
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2020 Sponsor 2019 Sponsor

    cordele, Ga.
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    Carb backfire (spitting) is a lean condition indicator which can also be caused by a lack of fuel. When you go to full throttle you are asking for max fuel. If the fuel pump is not able to give sufficient volume (albeit good pressure) then you will have a full throttle lean condition. This can also be caused by the power valve piston assy in the 2 jet carb not working properly. JMO
     
  14. Feb 29, 2016
    Angel

    Angel New Member

    New Salem, NC
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    Feb 10, 2016
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    Walt, the more I thought about it last night, the more what you said made sense. It would run 80 MPH last year. I decide to remove the carbs bronze filter out to see if that was holding fuel back and I drove it for 45 minutes, barely goes 45 uphill kicking and sputtering. I and going to tripple check my TDC and distributor position first, then take the carb apart again and go through it with a fine tooth comb. I don't have a known good carb to say this one is right. I have had known good parts for the distributor and rest of possible components. I have not checked my fuel pressure but the see thru fram filter is full with no bubbles at idle and WOT while parked.

    I did not replace my power valve or piston assemply and they seemed to be in good working order.
     
  15. Feb 29, 2016
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2020 Sponsor 2019 Sponsor

    cordele, Ga.
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    Realize that pressure and volume are not the same. A fuel pump can build a lot of pressure but with a small amount of volumn. Remove power valve and blow compressed air through bottom of carb at power valve hole.
     
  16. Mar 1, 2016
    Angel

    Angel New Member

    New Salem, NC
    Joined:
    Feb 10, 2016
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    Back to timing! I put it at TDC marked my #1 on the distributor, Oreiley's dist 30-1611, Says 1110376 on side. BWD Rotor # D146 and CAP #C175. New wires, tested spark to all cylinders using the timing light. It all looks good. I have times it with the #1 in the 5 o'clock position and the number 1 in the six o'clock position. It runs the same. I Know in an even fire, you can place it anywhere clock wise, as long as the rotor points to #1. Even at low fuel demand, there is some poping in the carb. Am I a tooth off? It will start easy and dwell, timing, rpm, vacuum guage all set and runs fine at idle. Give it a lil gas and let the popping begin. I beleive I have all the right oddfire parts, right? I cleaned the carb with the Harbor freight tool....Blew all the passages with compressed air and some were clogged. The accelerator pump rubber was broke. it has a ball at the bottom and that passage to the main float was clogged really bad. I made 200% sure that every passage was clear, tested vacum going to the dist and it's pulling well. Any thoughts on the one tooth off experience?
     
  17. Mar 1, 2016
    Angel

    Angel New Member

    New Salem, NC
    Joined:
    Feb 10, 2016
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    timed one tooth back from the 5 oclock, had to turn the distributor to get it to run and match the #1 on the cap, no change... Can't go any more back Advance is hitting the pulley.

    Found oil coming up the shaft of the distributor, Getting a replacement tomorrow...

    In the mean time, I took the carb apart and tested using mike carb parts troubleshooting. Seems fine, blew out every little passage, coild not find anything wrong, thre it back in with that suspected bad distributor, no change.

    Either I am doing something wrong, or I have become and expert ad dropping in the distributor at different clocking, 4,5,6.. It all runs the same, excellent idle, backfire on acceleration. getting new platinum plugs and replacement distributor tomorrow, can't work on it till Thu tho!
     
    Last edited: Mar 1, 2016
  18. Mar 4, 2016
    Angel

    Angel New Member

    New Salem, NC
    Joined:
    Feb 10, 2016
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    16
    Oreiley's tried to give me a distributor with the wrong casting number, then Oreiley's said the casting number didn't matter. I quickly pointed out the 1/4 inch difference in distributors so they ordered another. Got the new dist in, same problem, read that the PCV can also make it go lean, blocked it, it ran worse. Put in new Platinum plugs, same. Time to remove the valve covers and see if there is anything obvious. Anyone local want to test my carb out?

    Took it out on a test run and it seems like the Platinum plugs made it worse, Zero power now. This is with a fresh oil and filter change. Any ideas?
     
    Last edited: Mar 4, 2016
  19. Mar 4, 2016
    Warloch

    Warloch Did you say Flattie??? Staff Member

    Falcon, CO
    Joined:
    Mar 4, 2003
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    4,703
    With everything you have done, have you tried putting an electric fuel pump in to play? I'd go to where it was running good and add that to see if it will ID the lean condition it sounds like you have.
     
  20. Mar 4, 2016
    Angel

    Angel New Member

    New Salem, NC
    Joined:
    Feb 10, 2016
    Messages:
    16
    I already returned the prestolite distributor for the core. I don't think that's it, I'm on the third distributor and same problem. Waiting on this YouTube video to load so I can post a link, My camera can't take 1mb pics, lowest it will go is 2.5 MB. Do you have a part number for an electric Fuel pump?
     

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