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Backfire Help

Discussion in 'The Hokey Ass Message Board' started by dapirate, Dec 7, 2013.

  1. henryj1951
    Joined: Sep 23, 2012
    Posts: 2,304

    from USA

    bent push rod/timing/carb,ex

    Last edited: Dec 16, 2013
  2. dapirate
    Joined: Jul 25, 2013
    Posts: 77

    from Alpharetta

    ok my buddy told me drop some water on the headers while running.
    The good cylinders water drops immeadiately sizzle and evaporate
    Cylinder 1 water runs off
    Cylinder 4,6 some sizzling some water run off
    Cylinder 7 sizzle more than 4,6 but not like the good ones.

    Not sure if this helps

    I think I will get a infrared thermo gun from the store.
  3. That's an indication of not not converting fuel to the same heat energy as the others or those cylinders aren't working as well.

    Are the those plugs sooty, wet or fouled (not firing the available fuel) or ashy white ( not much fuel to fire)

    You could try screwing with the idle adjustment screw on the side that feeds 1467. Note the results. If there's no change that's a problem related to the carb.
  4. tjet
    Joined: Mar 16, 2009
    Posts: 1,275

    1. Early Hemi Tech

    Watched the video. How does it behave when you snap the throttle to WOT?

    To me, it seems like the timing is a little behind (retarded)

    Cool car :D
  5. dapirate
    Joined: Jul 25, 2013
    Posts: 77

    from Alpharetta

    I'd say the plugs all look normal except for #1 which was wet and black, not sure if it was oil or fuel, but if I had to guess I would say oil.
    I actually replaced 1 and it looks good so far, but of course I haven't driven it.

    I played with the left air adjustment on the carb and it does change the engine so I guess its ok?

    when you snap to WOT it Revs up with no issues. I only get the backfire on Deceleration.

    checked the temps with a heat gun after about 2 min on idle
    1 - 98
    3 - 224
    5 - 201
    7 - 170
    2 -178
    4 - 203
    6 - 225
    8 - 185
  6. As you can see, 1 is your odd ball and 4 6 & 7 are right even with 2358.
    So they must be doing close to equal work. Still puzzled as to why there's no change when they 467 are canceled, I can see #1 having little to no effect.
    I don't think this is going to help anything other than confirm #1 isn't as hot or having some troubles.
  7. olscrounger
    Joined: Feb 23, 2008
    Posts: 4,331


    #1 isn't firing--rest of readings look ball park--ck the valve adjustment on #1 amd ck for fire at end of #1 plug wire.
  8. Olderchild
    Joined: Nov 21, 2012
    Posts: 476

    from Ohio

    Rocker arm studs on #1 ??????????
  9. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    from Wisconsin

    My guess would be a vacuum leak on the intake close to the number one cylinder that is screwing up the mixture. If you set the idle up to 2,000, does the temperature on 1 match the other temperatures?

    As for the backfire, are the header gaskets sealing well? Back in the 60s it was hard to get them sealed and almost anything with headers backfired. It was why Joe started Mr Gasket.
  10. dapirate
    Joined: Jul 25, 2013
    Posts: 77

    from Alpharetta

    When I get home from work, I'll check the valve adjustment on #1 and inspect the headers.
  11. blowby
    Joined: Dec 27, 2012
    Posts: 7,769

    from Nicasio Ca

    Is that #1 wire resting against the headers?

  12. dapirate
    Joined: Jul 25, 2013
    Posts: 77

    from Alpharetta

    no, these are the MSD multi-angle wires you can actually bend to fit and its bent away from the header, and the rest of the wire is clear as well.
  13. King Karl
    Joined: Sep 27, 2007
    Posts: 384

    King Karl
    from N.C.

    Is the intake used?
    I had a similar problem a while back and ended up having a cracked intake manifold. Took forever to find the problem in that thing.
    Also, did you ever change the cap and rotor? Bad cap or rotor would probably be my first stop with this type of issue.
  14. saltflats
    Joined: Aug 14, 2007
    Posts: 10,853

    from Missouri

    Did you put new plugs in and have number one foul out immediately?
    Did it hit on number one with a new plug?
    You can check for a intake leak in the lifter valley by removing the PCV start the engine and plug all the holes in the valve covers but one and hold your hand on the one open hole and see if the crankcase is building pressure or drawing vaccum if its drawing vaccum it has a leak in the lower intake gaskets if not than its ok.
  15. dapirate
    Joined: Jul 25, 2013
    Posts: 77

    from Alpharetta

    The intake is new, and the cap and rotor have been changed.
    New plug in cyl 1 is slightly fouled.

    I did what Saltflats suggested and with my thumb over the hole in the valve cover its drawing vacuum.

    So I guess I need to remove the intake and re-install?
  16. 1971BB427
    Joined: Mar 6, 2010
    Posts: 6,912

    from Oregon

    No, before I'd remove the intake, I'd double check the valve lash adjustments. It's always best to try the easy stuff first. Sounds like #1 might be a bit tight and not closing completely.
    Might also consider grabbing a cheap used stock points distributor off craigslist and drop it in to confirm the Pertronix is good or bad? I keep one around I bought for $10, just in case I need to test on a SBC or BBC V8. Had an MSD box fail me and a quick swap of the distributor helped me find the problem. Left it in while I had the MSD box rebuilt.
  17. Does the needle bounce on the vacuum gauge ?

    What's the reading ?
  18. KStewart
    Joined: Dec 17, 2009
    Posts: 46


    Your points need to be reset. Sounds like they are to close. That the first thing I would check.
  19. Where's the points in a pertronix ?
  20. dapirate
    Joined: Jul 25, 2013
    Posts: 77

    from Alpharetta

    I'll double check the valves on Cyl 1.
    I had the backfire before the pertronix ever went in.
    I removed the #1 plug, plugged the hole with another spark plug and saw spark so that would confirm the plug and wire are good.

    I also swapped the wire and plug with cylinder 3 and there was no change in symptoms

    I hooked up the vacuum gauge and it bounces between 15"-18"
    I thought with a leak it would be lower???
    Last edited: Dec 11, 2013
  21. A rhythmic bouncing is an indication of a problem.
    Dropping manifold vacuum isn't normal.
    There's another diagnostic link some place, it has gif files to show the gauge and what it means.

    It's quite possible you have a manifold leak under the manifold.
    I don't know which new manifold you have but the cheapY ones are know to have problems.
    Forget the name but summit sells them in the 100 range.
  22. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,912

    dirty old man

  23. dapirate
    Joined: Jul 25, 2013
    Posts: 77

    from Alpharetta

    I have the Edelbrock Air Gap.
  24. Ok, then the cheapy manifold problem probably doesn't apply
  25. McGurk
    Joined: Jul 13, 2011
    Posts: 85

    from Mid West

    Check for broken valve spring at location of bent pushrod.
  26. dapirate
    Joined: Jul 25, 2013
    Posts: 77

    from Alpharetta

  27. tjet
    Joined: Mar 16, 2009
    Posts: 1,275

    1. Early Hemi Tech

    That's where the broken spring suggestion make sense. Sometimes an engine problem will be visible at different times.

    Here's what I would do: Pull the motor & pull the intake & heads. You can make a decision on how deep you want to get into it, but at least with the heads off, you can get a real good look at what's going on. Once your heads are off, a machine shop can check them for you and give you an estimate if they see any issues. I've done many top-end rebuilds. It's a real easy way to bring back performance to a motor & fix any problems. You can also pull a rod & main cap to inspect the bearings. If the bearings look good, & the cyls look good (no ridge), you will be good to go.

    On a positive note, it's a good time install thinner head gaskets to bump up the compression & maybe a new (better) cam

    Maybe this engine had this problem before & it was the reason it was sold to you.
  28. Yes if it were a stick valve, it would show up low on the compression gauge.
    But think about what the vacuum gauge is seeing and what it shows.

    Ponder this : I'm just thinking out loud.
    If you had intake gasket leak at #1 runner,
    The gauge would be show lower vacuum than normal
    every time # 1 was on its intake stroke the manifold vacuum would drop
    #1 would be sucking oil.
    Your vacuum signal to the carb would be low causing lean condition.
    Un accounted for air entering the system would cause a lean condition.
    In general, backfire on deceleration is caused by a lean condition.

    Exhaust leaks can cause a lean condition too because it effects scavenge and scavenge is directly related to cylinder filling efficiency.

    I'm just thinking out loud here for you.
  29. dapirate
    Joined: Jul 25, 2013
    Posts: 77

    from Alpharetta

    Before I changed the #1 cylinder plug it was fouled black, not sure if it was oil or what. So does that point more to the intake?

    If I have to pull the engine, I'd most likely go back with a 350 or a vortec 350.
  30. Well if a compression test for # 1 shows good,
    That eliminates a bunch of causes for oil getting in.

    What's your plugs gapped at ?

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