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  •  » 1970 STOCK 351C with shaker and 4spd.......backfire

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    6/13/2022 7:41 PM  #1

    M1Mustang69
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    Registered: 5/17/2013
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    1970 STOCK 351C with shaker and 4spd.......backfire

    Hi all, I'm inquiring for my buddies 1970 Mach......2 carburetors, a 600 Edel performer and now a Holley 600DP experienced a backfire a few times a the rpm range of 3000-4000 range (hard to tell exactly) IN 4TH!

    I can speak first hand with the Holley there is no hesitation, no stumble and ALWAYS appears/feels like there is enough fuel......."smells" slightly on the richer side even.

    Any thoughts on the most likely culrpit?

    I'm thinking timing.




    Oh, also, intermittent pinging which only appeared to be in 3rd at a conservative speed, but as you tend to "lean into" telling the car to accelerate, shortly there after pinging goes away. 

    I checked the Vac. adv and it's not working.....the canisters holds air, but does not advance the dist.  (It is also the dual canister type)

     

    6/14/2022 5:56 AM  #2

    TKOPerformance
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    From: Newark, DE
    Registered: 12/15/2014
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    Re: 1970 STOCK 351C with shaker and 4spd.......backfire

    My thoughts would be timing as well.  I would start by verifying that TDC on the balancer is actually TDC #1.

     

    6/14/2022 8:39 AM  #3

    Raymond_B
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    From: Fort Worth, TX
    Registered: 4/01/2013
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    Re: 1970 STOCK 351C with shaker and 4spd.......backfire

    Plugs will help tell the story, but for sure check the base timing. From there is really sounds like it's going lean in the higher RPMs. Might also want to check fuel pressure and float level.

     

    6/14/2022 10:44 AM  #4

    6sally6
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    From: Surfside Beach,SC
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    Re: 1970 STOCK 351C with shaker and 4spd.......backfire

    MOST of the time.... guyz carb issues are fixed by playing with.........the timing.
    I'd start the process with new plugs and wires maybe.
    Dual canister????.....All I've ever "heard" about those are 'issues'.
    (KISS should apply here....get a plain old Duraspark with the right type of gear for the cam he has.....)
    Go inside the distrib and install lighter springs for quicker advance.
    VERIFY   TDC and install a timing tape (very impotent!)
    With idles at 1000-1200 RPM...twist the distrib to get 36* advance looking at the timing tape with a timing light.
    Lock-it-down and RE-install the vacuum advance that is plugged into full vacuum (NOT ported vacuum)
    Go for a spin and see what happens!
    Tell your buddy to wipe that big stupid grin off his face...this is how Clevelands are suppose to run!
    BUTT.....this is just the starting place...
    IF the missing is now 'missing'..... try more advance........or less.  With a test drive after each adjustment.
    (This is assuming.. there's not junk in the fuel tank...new filter etc.)
    6sally6

    Last edited by 6sally6 (6/14/2022 10:44 AM)

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    6/14/2022 1:03 PM  #5

    BobE
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    From: White Plains, NY
    Registered: 4/04/2013
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    Re: 1970 STOCK 351C with shaker and 4spd.......backfire

    In addition to the above suggestions, don't rule out a possible bad valve, suggest performing a compression check to verify cylinder pressures are all equal. 

    65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
     

    6/15/2022 1:16 PM  #6

    M1Mustang69
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    Registered: 5/17/2013
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    Re: 1970 STOCK 351C with shaker and 4spd.......backfire

    Thank you everyone. 

    I can't imagine lean, it's a Holley and I have 66/68 jetting with a 6.5PV. A completely stock motor that's a decent amount of fuel!  Zero performance/driveability issues start to 4th at 110miles an hour, with the exception of a random Spit/Back fire out the carb from 3500-4000rpm.  It does not do it consistently. 

    We gotta verify the Timing (I know it was checked recently but I only trust myself). 


    One last question, His Dist. Had a PerTronix D-57-22 elect. Ignition.  Can I use anSD Blaster 2 coil directly to it?

       •Thread Starter
     

    6/15/2022 2:54 PM  #7

    MS
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    From: Canyon Lake, Texas
    Registered: 1/24/2013
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    Re: 1970 STOCK 351C with shaker and 4spd.......backfire

    Start by fixing the vacuum advance.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    6/15/2022 5:17 PM  #8

    TKOPerformance
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    From: Newark, DE
    Registered: 12/15/2014
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    Re: 1970 STOCK 351C with shaker and 4spd.......backfire

    M1Mustang69 wrote:

    Thank you everyone.

    I can't imagine lean, it's a Holley and I have 66/68 jetting with a 6.5PV. A completely stock motor that's a decent amount of fuel! Zero performance/driveability issues start to 4th at 110miles an hour, with the exception of a random Spit/Back fire out the carb from 3500-4000rpm. It does not do it consistently.

    We gotta verify the Timing (I know it was checked recently but I only trust myself).


    One last question, His Dist. Had a PerTronix D-57-22 elect. Ignition. Can I use anSD Blaster 2 coil directly to it?

    I would only use a Pertronix coil with the Ignitor.  If you read the fine print there is concern about resistance values, etc. that only the Pertronix coil seems to satisfy.  The Ignitor is meant to be used with a stock coil, and it seems a typical performance coil could cause issues. 
     

     

    6/17/2022 8:11 AM  #9

    MS
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    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 11,725

    Re: 1970 STOCK 351C with shaker and 4spd.......backfire

    Remembering wwaaaaayy back, I had a 70 with 351 in it with points distributor. As the coil heated up, it would start cutting out like that. A new coil fixed it.  Later, I would be driving along at speed and it would backfire and then quit completely. That turned out to be the condenser in the distributor.

    Shortly thereafter I discovered Duraspark ignitions and have never had distributor problems again.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

     

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