My 1977 XLT had been running super crappy. After a warmup and being sure the choke was full open, when I was running at about 25MPH, I mash the pedal and she goes POP BANG POW. First I checked the timing and set it to 10 degrees BTD. Same thing. So I went out and bought and installed a brand new set of wires and new plugs. It is much much better, but there is still one Pop although not quit so powerful an explosion.
I suspect timing is off.
So here finally is my question. About 10 years back, when I had the aluminum water pump cover rust and fail, I changed the timing gears and chain. I read up and installed the gear set from a 428. Reason being the 460 had the factory crap set that made poor power. The factory crank gear had the alignment dot set 1/2 tooth off TDC. Which made for 4degrees off TDC on the crank equaling 8 degrees out on the cam.
So what I am asking is..... After changing the gears, do you use the degree marks on the pulley as they were or do you have to compensate and advance or retard the timing to compensate for the changes you make to the gears.
I feel for sure the backfire is spark related and really want to get back to NOW POWER when I mash the go.
I know for sure one of you guys has the simple answer to where to set my distributor.
So thanks.

 

Maybe wount be in your case but my 300 I6 also backfired. After going through same steps as you I found a very small vacuum leak. After fixing the pipe no backfire since.

 

It was probably an early 460 (or 429) chain. The later years retarded the camshaft for emissions so the install of earlier style (1970 and earlier me thinks) timing chain and gears is common upgrade.

Your timing should be set at 8-10 degrees as per stock specs. Timing would have to be out a mile (ie timing chain jumped a tooth) to cause what you are describing.

Sounds more like a lean fuel condition. As was previously mentioned, it could be something as simple as a vacuum leak somewhere (check all your manifold plugs as they like to blow off when a backfire occurs) or low fuel pressure / carb problem. Check for vacuum leaks and then check your fuel pressure. Change out any fuel filter(s) and go from there.

 

I'm assuming its a 4v. First things to check would be is the primer working properly and also see if the secondaries are closing tight. Next check the vaccum it should be around 18. If every thing looks good and there is not any vaccum leaks make sure your advance is working properly. Not knowing the mileage but if its high it could be a wore can lobe but I would be more toward a intake gasket or carb gasket. Good luck I know its a pain

 

Being that the accelerator pump is inside the carb, best bet would to buy a kit, find a carb guru and have the kit installed "correctly" Every time I try a carb rebuild I usually loose all the teeny tiny parts or end up with about half the kit left over. Those who do bench vacuum testing are all gone due to the days of fuel injection.
Today I checked all the vacuum lines and there not leaking. I replace the tripple vacuum tree connector that is on the heat activated switcher thingy. It was all cracked and spongy. It is the switch that draws from one source when the engine is cold then changes to another source when the engine warms up. I also pulled of the line that runs to the vacuum advance and it holds its position until I stop sucking on the line. So the vac advance is doing as it should. As a test I connected the distributor port directly to manifold vac. engine ran well but still had the Pop Pop when at WOT. Mind you just one backfire maybe two, and then nothing but power.
So everything is pointing to the mentioned lean fuel mixture. Caused buy just not enough gas getting to the engine. Also whenever the if truck has been left sitting a week or two it has to crank and crank before it starts and runs. Once it fires its smooth as silk immediately. Thats telling me the carb is draining down when not used. Possibly the float is done. So all things point to a carb rebuild. Now I have to find someone who's good at something that has gone the way of the dinosaurs. Also need to find the kit. Direct to Ford will have to be my start point.
Oh as mentioned the mileage on the truck is currently 117500. Very low in miles but very long in the tooth for age. Dont know if the carb has ever been rebuilt. My dad bought the truck one year old, when it had 5000 miles and Ive had it for about 15 years. It is a full load with air, cruise, deluxe two tone paint and the XLT luxury interior package. Ive never touched the AC and it still blows ICE cold.

 

Sounds like the carb could use a freshing up. Honestly carbs ain't bad to rebuild I kind of like redoing them (I know I'm nuts) but as mentioned its a dying art. The trick is to clean clean clean! If you can adjust one you can rebuild it and it be right unless its a qaudrajet .. What carb are you running by the way? Oh and you may want to check the fuel pump psi if it hasn't been replaced. I've seen them do crazy things to any engine and thought it was a bad carb and it be a very weak pump. Especially if it has some sitting time.

 

Thanks for the advice. The carb is stock ford autolite 4v. I can get the kit in town for $55 then bless our government with another 10%. So thats really not bad. Add in some for a gallon of carb cleaner, and a 750 bottle or Rye for my neighbor whom is a retired mechanic and I should be good to go.
The fuel pump is also a good place to start. I replaced it about 15 years ago, but the truck sits a whole lot. Here in Canada as of today were paying $1.25 per liter of regular gas. So thats 1.25 x 3.78 lts per U.S. gallon equals $4.76 per U.S. gallon. So the truck is not a daily driver and does sit a lot. Then again the 26 of Rye here also costs us 30 bucks as opposed to your $10, and yes we do drink a lot. Gee its great to be in Canada

 

Good to see that you are gathering all necessary materials and uh, "shop supplies" prior to the work being performed.