My car has a slight popping coming out of the exhaust. What causes this and how can I fix it?

Possibly bent or burnt valves?



[This message has been edited by CopperTop (edited January 05, 2005).]

If you are running a 78 like your name suggests, and you still have the original carb, it is running too lean, especially if you have added a better air cleaner or a better exhaust system.

Anytime I have exhaust popping, it ends up being from a factory carb that it too new (75 or later) to run rich enough to handle any mods that add horsepower.

Carbs from 70 and prior just don't do this. Starting in 71, carbs were mucked up for emissions, and from about 71-74, they were usually still rich enough to avoid this problem, but didn't perform like 70 and earlier carbs. From 75 and later, factory carbs were too lean to handle any engine mods like better breathing air cleaners and exhausts that lean them out even more. Exhaust popping usually comes from a too lean condition that causes an engine to misfire at idle or under de-acceleration.

The easiest way to help this problem is to keep the primary throttle plates open farther during idle and during de-acceleration. To achieve this, you need to retard the timing to lower idle speed and then compensate with the idle screw to open the primaries more to achieve the correct idle speed. The flipside of doing this is that retarding the timing will seriously hurt performance and mileage, so it isn't practical to do.

There is one "cheat" that sometimes works. If your factory carb is currently running full manifold vacuum, and your carb has a ported vacuum port, you can move to the ported port, retard the timing to get the correct idle back, and you get your performance, your mileage, and also get the carb to idle and de-accelerate with the primaries farther open and burn the gas so you don't have the popping.

A lot of times popping out of the exhaust is a misfire due to poor ignition. First things I'd check would be ignition related items. Wires first, plugs, rotor and cap. Easy way to check the wires is to pour water over the wires from a jug or a hose. They will arc and you can hear them snap plain as day. If they are old and crusty replace them anyway.

------------------
70 SS 454 CI Dynoed 684 HP, 702 TQ All Aluminium Fuel Injected Small Block , plus 200 - 500 HP NX nitrous system.

<font face="Arial,Verdana" size="2">Originally posted by Gary S:
If you are running a 78 like your name suggests, and you still have the original carb, it is running too lean, especially if you have added a better air cleaner or a better exhaust system.

Anytime I have exhaust popping, it ends up being from a factory carb that it too new (75 or later) to run rich enough to handle any mods that add horsepower.

Carbs from 70 and prior just don't do this. Starting in 71, carbs were mucked up for emissions, and from about 71-74, they were usually still rich enough to avoid this problem, but didn't perform like 70 and earlier carbs. From 75 and later, factory carbs were too lean to handle any engine mods like better breathing air cleaners and exhausts that lean them out even more. Exhaust popping usually comes from a too lean condition that causes an engine to misfire at idle or under de-acceleration.

The easiest way to help this problem is to keep the primary throttle plates open farther during idle and during de-acceleration. To achieve this, you need to retard the timing to lower idle speed and then compensate with the idle screw to open the primaries more to achieve the correct idle speed. The flipside of doing this is that retarding the timing will seriously hurt performance and mileage, so it isn't practical to do.

There is one "cheat" that sometimes works. If your factory carb is currently running full manifold vacuum, and your carb has a ported vacuum port, you can move to the ported port, retard the timing to get the correct idle back, and you get your performance, your mileage, and also get the carb to idle and de-accelerate with the primaries farther open and burn the gas so you don't have the popping.</font>

When I first got my car it was all stock with the original 2 barrel. When I tried to use a free flowing open element air cleaner it leaned it out so bad I couldn't drive it. A lean idle mixture will make it sputter out the exhaust, as will any ignition problem or a valve that isn't seating.

All of these responses are correct. It could be valves adjusted too tight. We need more info to further diagnose this, or all anyone can do is guess. Can you tell us anything else about the problem? Have you made any repairs, mods, or done anything at all to the car lately? Be as specific as you can be. From what I have seen on this board, there are some really sharp folks on here, and they are more than willing to help.

------------------
I thought this was supposed to be fun?!