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Over - run Backfiring ?

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  #16  
Old 08-10-2018, 11:41 AM
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Matt, I agree with you (see post #4) and the issue will not be fixed with a timing change. Quit a few motorcycle carbs are outfitted with a de-acceleration diaphragm that slows down the closing of the venturi which prevents the rapid lean condition that results in the backfire.
 
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  #17  
Old 08-10-2018, 12:07 PM
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In the ninth entry to this thread, the OP informed us he is running dual 97s. Who knows what his fuel ratio might be, , what other mods the engine may have, or where the problem may be originating. Unless the after fire is so bad it is raising the ire of the local LEOs or significant other, live wth it.
 
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Old 08-10-2018, 12:31 PM
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Since this doesn't have a stock intake, or carbs, I have to wonder if the PO blocked the heat riser ports. Some dual carb manifolds don't have any riser passages. When you do that on a flat V8, it makes it pop thru the exhaust just as described.
 
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Old 08-10-2018, 03:20 PM
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I agree Ray. He said it goes away with a little throttle so that would be the EASY way to fix it if it causes concern.
 
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  #20  
Old 08-11-2018, 01:46 AM
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Well I think I will start then with richening up the fuel mixture just a little, and see how it goes. It is not a real problem I guess, I was just curious to know what the cause might be. Thanks to all again, and hello to Limey.

Suffolkman
 
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Old 08-11-2018, 08:52 PM
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Does your backfiring sound like this on my 54 F100 with the 239 Yblock? Notice it goes away when I hit the gas.

Both my trucks have glass packs and rumble on deceleration, the 54 a bit more so than the 55. I thought it was part of the cool factor.
 
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Old 08-11-2018, 08:55 PM
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Here's coming down the mountain, part 1

My son and I were in my truck. The wife, a friend and sister in law were in the car filming. Listen to their comments.
 
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  #23  
Old 08-12-2018, 03:15 AM
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Originally Posted by abe View Post
Does your backfiring sound like this on my 54 F100 with the 239 Yblock? Notice it goes away when I hit the gas.
https://m.youtube.com/watch?v=uY4N8tkx7Hs

Both my trucks have glass packs and rumble on deceleration, the 54 a bit more so than the 55. I thought it was part of the cool factor.
Yes exactly like that.
 
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Old 08-14-2018, 06:52 AM
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Originally Posted by abe View Post
Here's coming down the mountain, part 1
https://m.youtube.com/watch?v=9sm1473j3xE

My son and I were in my truck. The wife, a friend and sister in law were in the car filming. Listen to their comments.
I think its a nice feature. Keeps the tailgaters away. BTW. Thats a beatiful truck you have Abe!
 
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Old 08-14-2018, 07:19 AM
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Thank you all for your comments, ideas and advice. The general opinion is I think, that it is not to much to worry about, I think I will just let it be.
All the Best from England.

Suffolkman
 
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  #26  
Old 08-14-2018, 07:29 AM
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Originally Posted by Suffolkman View Post
Thank you all for your comments, ideas and advice. The general opinion is I think, that it is not to much to worry about, I think I will just let it be.
All the Best from England.

Suffolkman
Do not think i would go so far to say that, it is pretty hard on valves and seats and can lead to fractured valves over time.
 
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Old 08-14-2018, 09:58 AM
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Originally Posted by hooler1 View Post
I think its a nice feature. Keeps the tailgaters away. BTW. Thats a beatiful truck you have Abe!
Thanks Hooler.

"Keeps tailgaters away".... You heard my wife's friend say, "it sounds like fireworks."
 
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Old 08-14-2018, 10:18 AM
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Originally Posted by matthewq4b View Post
Do not think i would go so far to say that, it is pretty hard on valves and seats and can lead to fractured valves over time.
Please explain.
 
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Old 08-14-2018, 10:39 AM
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I would agree that it's a "feature" if it sounds like that. The poppitypop on decel from a more open exhaust is common. Heck, my Jag is designed to do that :P

Unless you're getting loud pops or bangs and you can "feel it" (ie: scares the bejeezus out of you or others), I wouldn't worry about it. Nor would I worry about any damage to the engine components. When things feel like they are "exploding" internally, then I would investigate.
 
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Old 08-14-2018, 10:52 AM
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Originally Posted by raytasch View Post
Please explain.
In bikes when excessive it has been known to cause valves to fracture on occasion. I;m not sure if it is from the repeated reverberation from the after fire or what but valve failure has been linked to excessive after fire..
As for the seat , with afterfire you can force gasses past the valve and seat as the valves were not designed to seal in the reverse and this will over time erode the seat/valve.
It has even been linked to bent rods on occasion in some applications (2 strokes)
Not to mention how hard it is on exhaust components.

Afterfire should be mitigated as much as possible either by richening up the idle air and/or backing off base timing and allowing for the butterflies in the carb to be open more at idle.
This is another reason why not to run manifold vac for the dist vac advance on street motors.

Either way afterfire should be mitigated as much as possible . The manufacturers went through great lengths to mitigate it once it became apparent how damaging it actually was over the long term.
 
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