I concur. Great video abe but I would encourage you and Suffolkman to fix this condition before real damage occurs.

 

OK, you have me concerned. But if my truck did not do this on decel when I had a muffler on it and then it does it with the glass pack it would lead me to think that it is an exhaust issue, not an internal issue.

 

 

I used to do that in the F600 and F700's I drove in 72-74 when I worked for a lumber yard. I did it when I saw people I knew on the sidewalk. One of the older men there said I shouldn't do it in the company trucks.

So Kevin, a little poppity-pop out the tail pipe with a glass pack is OK? Whats your opinion?

 

 

Many trucks of old did the exhaust pop, afterfire, when loaded and geared down while descending a hill.

 

I could not agree more. After a thousand years of constant exhaust-popping (back-firing is through the carburetor - hence the name) you may develop a heat stress crack in the valve neck.

 

 

It does not take a thousand years for afterfire to fracture valves. In this case 19K miles was just enough.
Enjoy the poppity pop but just be aware it comes with risks.

 

I don't think it is reasonable to apply a phenomenon that occurs in modern, fuel-injected, high-revving engines, to our old trucks. I don't even know how you could get an old Ford truck to run lean, they run way too rich if anything.

 

It is easier to be honest in a carbed engine. Modern fuel injected engines monitor the actual fuel air ratio and adjust the injector pulse width to either richen or lean the fuel being delivered to the cylinder at all engine rpm's. Unless you make changes drastic enough to change the volumetric efficiency beyond the programming of the ECU that the computer can compensate for it or the injectors are maxed out in their ability to provide more fuel.

Non feedback carbs can not adjust the fuel air mix it is fixed with the main jet and the idle air mix adjustment. Even feedback carbs cannot adjust the idle air mix.
When you improve the volumetric efficiency of an engine either by uncorking the exhaust or some other means this allows for more air to enter the cylinders at any given throttle position, adding more air (oxygen) means you need more fuel to keep the same fuel air ratio. If you do not adjust the carb's jetting or Idle air mix (for running on the idle circuit) you will run lean and we all know what happens when you run an engine too lean.
The afterfire on deceleration is a lean condition backfire. It's no different than a lean backfire/ miss at speed or idle. It's funny how people will tolerate an afterfire due to a lean condition and think it does no harm but will go through great lengths to prevent it at idle, under acceleration, or during cruise , cause of the damage it does.
That afterfire on deceleration is your engine screaming at you for more fuel.

 

Me thinks this thread is a bit blurred. Here we are discussing backfire and after fire in the same context.

I would suspect the valve shown above has been leaking for many miles or hours, burning, eroding a bit more each power stroke of the engine. I have to wonder if this is 19K miles from new or on a rebuild, or what. Either way, that engine had to have been running like crap, the cylinder was essentially dead and had been that way for a long tme. An early valve adjustment may have prevented that carnage.

I was of the impression that with newer technology fuel systems, fuel is pretty much shut off when the vehicle is in the coast or decelerate mode.

 

This is typical afterfire failure of a valve cracking on the back side leads to prorogation to the face that eventually blow torches through the valve. Some more afterfire failed valves below. Valves are not designed to be forced open by the backside of the valve face, not to mention the backwards heating stresses on the valves encountered with afterfire.. The above valve fractured then blew through when the fracture propagated to the valve of face. All the valves in the engine exhibited back side valve fractures. These failures happened 19K on a brand new motor that had the exhaust uncorked and after fired on decel. Valve cracking due to afterfire is well documented there really is not much to contest here. You would not run engine lean at idle under acceleration or at cruise. Not sure why people would think it is ok to do during deceleration.

 

Was the valve above from a flathead or a Y-block?

 

Interesting pictures. Are those valves from a desmodromic valve set up, by chance?