backfire

[fryedaddy]

i took the 2bbl carb off my f250 and took it apart and cleaned it. very gummed up inside. i put it back on,problem is now it backfires out the exhaust every few seconds depending on how much throttle i give it.what did i do wrong?

[1964Fastback]

My first thought was maybe an exhaust valve is sticking/gummed up.  Maybe pull one spark plug wire, test, put that wire back on and pull the next one to see if it's always the same cylinder.  The other thing I thought of is maybe it's idling lean (or I guess could be rich) causing some unburned gas to make it through to the exhaust where it gets lit and explodes there from time to time causing the backfire.

Go over the basics first like float level, timing and idle mixture to see if it can be tuned out.  Does it do it when driving it?  If so, that kind of rules out just the idle mixture I guess.

Pat

[fryedaddy]

the truck has been sitting for a few years,i have not driven it yet.at idle it might backfire every 5  or 10 seconds,if i rev it it backfires louder.i dont have all the bugs out of it yet.it needs a complete tuneup.all i did was oil change,plugs,sanded the points and cleaned the carb 3 times.it did not backfire till this last time i took it apart and cleaned it.the fuel pump is questionable,it fills the carb but it dont have much pressure.you have to prime the carb with a few ounces of fuel to get it to start.but once its running it will stay running

[shady]

 exhaust manifold leak will make it backfire. get a rebuild kit for the carb.

[gdaddy01]

accelerator pump not working, too much air when you first open the throttle?

[fryedaddy]

i did put a new accelerator pump diaphragm on it,but it still refuses to pump gas out of the squirter holes

[Stangman]

So it didn’t backfire before, possible bad or wrong gasket going together. Maybe vacuum leak around base gasket? Did you check to see if it’s dumping or dribbling fuel. How about timing did you play around with that while you were doing carb.

[fryedaddy]

after just a couple days my acc. pump diaphragm started coming apart.i noticed when i bought it at the auto parts store yesterday it had a gooey looking glue on it.i even pulled a little of it off before i put it on my carb.could it be i bought a faulty pump. i havn't touched the timing.

[fryedaddy]

i took my carb apart again,cleaned every spec of junk i could find in the nooks and crannies,for now i had to put the bad acc pump diaphram back in.its hard to start,but once its running it sounds good,no backfire.i took the jets out and cleaned under them,i think it was plugged underneath them.the backfire must have been a lean condition?