does this logic make sense?

[lasadoor]

Bronco was running rough, backfire out the exhaust, and stalling. I cleaned my spark plugs, adjusted the idle speed screw 1 1/2 full turns from where the screw makes contact with the flange, and then adjusted the timing to 6*btc. now she seems to be running good again.

so near as i can tell the engine wasn't running fast enough to produce a strong enough spark to burn the fuel in the cylinder. is this correct or am i way off?

 

[DuctTape]

So I had an exhaust backfire issue last year. I did a bunch of research.

A backfire in the exhaust is because unburnt fuel has gotten into hot exhaust.

But it turns out there are many things that can cause unburnt fuel in the exhaust. Wrong timing, too rich carb, insufficient spark are the key culprits. I've seen some people say that too lean can also cause it as well as problems with compression or valve train issues.

Wrong timing, too rich carb, and insufficient spark all have more than one possible cause. Since you tweaked the spark and timing at the same time it is hard to tell which one was the problem.

 

[lasadoor]

maybe she was just feeling sensitive and needed some love

seriously, i suspect it was a little bit of everything, but i'm always eager to learn as much as i can

 

[broncnaz]

It was probably mostly your timing that fixed most of the issue. If the idle was rough then turning the idle mixture screws may have helped a little to.
Putting the idle mixture screws at 1 1/2 turns from the seated position is only a baseline setting that gets you in the ball park. Generally you can tweak them from there and get a even better idle. your looking for the highest steadiest idle you can attain. (a vacuum gauge helps here).
Usually you can run more than 6 degrees of timing kinda depends on your igintion system tho. Also if you have points as they wear the timing changes so you may want to adjust/replace them and reset the timing.

 

[Joe473]

If you are still running points check them with a dwell meter. Bad or points going bad will cause backfire.

 

[lasadoor]

No more points for me. The last set came apart inside the distributor cap right outside O'reilly Auto. Proper timing and tweaking the idle speed seem to have fixed the issue. Thanks for your help. Onto the next project...