and how do i fix it?

im getting some off-idle backfiring through the intake and im trying to figure out what i can do to fix it.

thanks in advance

timing.

valve timing or a bent valve?

What causes backfiring thru the intake manifold is the spark plug firing the A/F mixture when the intake valve is still open....

That can be caused by extremely low base ignition timing or a bent intake valve or an improperly adjusted intake valve (lash too tight).
Will

Check for any spark plug wires "jumping fire". Also check the distributor cap for small hair line crack inside, and for carbon tracking.

Joel

A intake valve hanging open would be the most common cause as mentioned. On flat tappet engines, if it pops back thru the tb at full throttle, the cam is going flat. And if the engine is extemely cold and the A/F ratio is was lean, they can pop back thru the carb or tb when cold. And also ignition problems as mentioned

How old is the distributer and cap. I had a similar problem on an 84 and it ended up being a bad distributer. Ran great after that.

If it also has trouble at WOT it can be a week ignition/ low voltage. It takes more energy to fire at higher compression pressures.
If it does it at all rpms it can be the valve train. It is a fixed relationship. Has it been over reved?
A carbon tracked cap will usually have issues at all rpms.
Arcing plug wires sometimes show up in the dark.
If it sputters like you need a new accelerator pump when you give it a little gas but runs fine if you punch it, it can be a worn throttle position sensor with a flat spot in it.
Tech