ehaust backfire

Usually back fire through the exhaust is running too rich.
May need a carburetor or FI tune up such as O2 sensor.

Need a shop that has a smog machine to check the mixture.

Since in your other post you say you have a broken manifold, a large enough leak there can cause back-firing.

Doubt that would cause a stumble though. I would start with a full tune-up and search for any vacuum leaks. It's also likely your Oxygen sensor is bad by now (even if it doesn't throw a code) and the EGR valve is likely sticking (bad design).

Sometimes ignition switches become worn especially if they had a collection of other keys and stuff hanging from them.

If the contacts momentarily disconnect and the ignition quits and then resumes the gases explode in the muffler.

I've found them by connecting a 12 volt bulb to the ign side and see if it flickers or goes out momentarily.

Check for fault codes. Is the check engine light on? To get more definitive information/help, you really need to provide more info about your vehicle. Under what conditions does it stumble/backfire? Cold, warm, full throttle, idle? Accelerating, constant speed? At what speed? Things like that.


Chum lee