Expert: Vern Bullock - 3/8/2008

Question
QUESTION: why does my 283 engine back fire?

ANSWER: Hi Janet:

Normally backfiring is caused my too rich of fuel mixture. Lack of air in the fuel mixture causes unburned fuel to burn in the Catalytic converter becasue the piston(s) maybe starveD for air. Also, a plugged converter can cause the same problem. Since I don't know the age of your vehicle, I can't say if the Cat is old and possibly plugged, but check the fuel mixture. You will either small gas are rotten egg type small. Hope this helps.

---------- FOLLOW-UP ----------

QUESTION: hi i wrote to u yesterday regarding my engine 283, chev 1957, back fireing and i changed the points do i need to change the condenser as well? thanks

ANSWER: Hi Janet:
I'm sure you don't drive it too often, so I would think all you needed for this tune up would be plugs and points. As long as it starts OK, I wouldn't replace anything else except maybe the spark plug wires. If you have a bad wire or bad wire connections, this could be fouling the plugs. So, check your wires and make sure they look in good shape and that the connection from the distributor to the plugs are metal-to-metal and tight.

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QUESTION: well the plugs arnt very old and the points are new? what else could it be? thanks

Answer
Hi Janet:
Did you adjust the carb first? In order to get rid of the backfiring, the first thing is to adjust the carb so it doesn't run too rich or too lean. Once the carb are adjusted, I would take her out the road to give her a good blowing out. If she was running too rich, the plugs would be a bit foul from all the excess gas being dump into the cylinders. Do this first and let me know the results.

She should run a bit rough at first, but should smooth out after driving her 20 to 30 miles at highway speed. If she still runs rough and is still backfiring, the problem could be a bad plug or plug wire. One thing for sure, one or more cylinders are NOT firing correctly.