Carburator

Does anyone know why my two barrel would misfire (backfire) through the carburator?  1966 Mustang 289 starts great, idles great but when the gas pedal is floored, it misfires through the carburator.  
thanks.  

check the dwell on the points with a dwell meter...  with the vacuum advance disconnected..

if the dwell is within spec...  and the condenser it properly tightened down...

check the spark plug wires at the cap.. that they are fully seated...



now.. engine off.. usually on a cold motor.. open the choke blade.. look straight down the throat of the carb... use a bright flashlight..   move the throttle lever.. do you get 2 nice streams of fuel from the pump discharge nozzles...


i have used some 0.023 stainless welding wire to show how the path is..



there is a WHOLE LOT MORE to learn about the autolite 2100 carb...  they are fairly simple to rebuild...  probably the easiest of all carbs to rebuild..   they are still a precision device and need to have each opening cleaned and checked that it really does pass spray..  

Assuming timing is correct, there is one main reason why an engine backfires and that is leanness. Like Wayne is saying, its probably the shooters(Accelerator pump discharge nozzles). They get plugged or the diaphragm that operates the shooters goes bad, check both. Too much accelerator pump will cause a black smoke from your tailpipe, too little will cause a hesitation and possible backfire as it goes lean for a few seconds. The engine dislikes a gulp of cold air without hydrocarbons.