Have a 1973 f100 with a FE 360 that was popping threw the carb when we got it, so we had the carb rebuilt and it still does it. We replaced the spark plugs and did a compression test and all cylinders came back with 130lbs each. Also replaced the points, condenser, cap and rotor
Any ideas on what it could be.

 

Condensers are junk today. Try to find a good NOS or known good used. Backfiring through carb can also be an ignition timing problem.

 

the original condenser we still have, we tried to advance the timing and retard it and didn't make a difference. It is drivable but when you quickly accelerate it falls on its face, under acceleration is when it pops it will idle perfect.

 

I was wondering about that. Any chance the timing chain has jumped a tooth or two? Backfiring through the carb is pretty much always a timing issue.

Make sure the plug wires are routed correctly and firing order is correct. This is a good thing to check (among others) when getting a "new" truck.

 

ok thanks, we were told by the previous owner he had thought it had jumped but with only 145,000 original miles weren't sure

 

Just a bit more info on why....... backfires through the carb is the result of an air/fuel charge being ignited with an intake valve(s) still open or open at the wrong time(ing). Makes sense, right?

"Only" 145,000 miles? It could be 245,000 or 345,000 since the odometer rolls over at 99,999.9 and goes back to zeros.

Unlike today's highly engineered/machined components with close tolerances and electronic engine control systems, engines in vehicles of this era typically require a rebuild at 100K miles.

 

Bad, cross firing plug wires could be the culprit also a bad coil. Like others said, there seems to have been a bad bunch of condensers popping up lately.
The compression test you did pretty much rules out a stuck valve.
From your description it could be fuel related also. You said that it falls on it's face when you accelerate and that's also when it pops. Check the accelerator pump, be sure that it's functioning. Pull the air cleaner cover off and look down the throat of the carb. Push the accelerator, you should see two strong squirts of fuel into the throat of the carb.

 

We changed the wires and put electronic ignition in it. We are able to time it so, the timing chain shouldn't be the problem? Is it possible we have a valve stuck closed

 

It wouldn't idle very well I'm thinking.

 

I don't think you would have had such even compression if you did, but an easy way to check, pull the valve covers and look for a bent pushrod.

 

Even easier connect a vacuum gauge to manifold, would be useful for troubleshooting.

 

I just went through something similar, it turned out to be bad plugs, even the new Autolites! NGK plugs cured the problem for about $18 and they aren't that hard to change

 

Forgot to mention after we did the compression test we put new plugs in it

 

What brand? have you checked them to see if they are fouling? I put several sets of new autolite plugs in and it didn't help, from what several people have told me the autolites aren't very good plugs anymore

 

they are autolites haven't checked them yet will do that next we work on the engine also going to check the pushrods out