I have a 79 f350 that I drive back and forth to work every day. I have been having some problems this past week. I hit alot of stop and go trafic and it acts up and starts missing at lower rpms but is fine after I get it moving(untill I have to shift). I was thinking it was like a vapor lock problem, becase it has been so hot (90 degrees) this week. but today it did something diffrent that changed my mind. It would backfire out the carb like its out of time and getting to mutch fuel. So at this piont in time I was looking for some oppinions on what you thought it might be

 

Backfiring = the timing is off, or if you still have the smog pump - it could be a bad air bypass valve. My money is on the timing. Possible causes...bad timing chain and gears, or distributor related.

 

How many miles do you have?

 

its showing 89562 but I cant tell you how many times it has rolled over, I checked the timming after I got home and let it sit for about half an hour and it checked out ok

 

When was the last time you checked out your cap and rotor?

 

about a day ago. they arnt shot but could stand to be changed, Im going to pick up plugs, wires, cap, and rotor tommorow

 

Might try adjusting the idle fuel - air mixture screws. Or maybe a vacuum leak. I would spray carb cleaner around the base of the carb and along the intake gaskets while it's running.

 

I replaced the vacume lines about a month ago so thats out, I dont realy want to mess with the carb yet

 

After reading your post a little slower I seen that you mentioned backfire. I can only think of a few common things that would cause backfire, igntion timing, valve timing (timing chain), burnt valve(s) ,shorted / miss wired plug wires, or a bad power valve in holly carbs.

 

I will have to check the timming again after running home from work without shutting it off when I get there, Ill let you know what I come up with

 

Also check the IGn module for a space behind it so it can cool.
These modules are notorious for failing in hot climates.

 

I will have to check that out, thanks

 

yall are gona like this, my problem turrned out to be from a bad battery. I checked things over sevral time and this afternoon the battry died and I put a new one in and it seems to have solved the problem, thanks for all your input

 

mine is also backfiring or poping once some times twice when slowing down to a stop from a cruising speed. would this also be the timming? advance or retard?

 

79 br...that would be your timing im sure...cause i have this issue with my 351m that i have to retime it almost everyday..to where ill be cruising or something and step on it and itll backfire out of the carb and it throws my timing off..so check your timing with a timing light and see what you come up with..