Engine: Puff of black smoke

[PeterHawk]

Just got back from a 300 mile run on the Interstate. My "chase car driver" said when I let off on the gas a small puff of black smoke came from the exhaust. Any ideas???
If you need additional details before commenting, let me know.

[karterfred88]

Just got back from a 300 mile run on the Interstate. My "chase car driver" said when I let off on the gas a small puff of black smoke came from the exhaust. Any ideas???
If you need additional details before commenting, let me know.

Black usually means too rich, blue-grey possibly worn valve stem seals, guides, or oil control rings allowing oil past on high vacuum, not on compression. The too rich condition is hard to fix on carbureted cars, as the vacuum caused by letting off sucks excess fuel past the jets no matter what you do. Can be minimized, but most carbed cars show some "puff" backing off and then being reaccelerated. If it otherwise doesn't "smoke" and runs well--live with it, unless your spark plugs start fuel fouling with black deposits, then it's time to go through the carb to prevent fuel washing on the cylinder walls. If its blue-grey you can change the valve stem seals "easily" in the car. Depending on age and miles on the engine, they would be the first item suspect as they harden up with time just sitting in your driveway, and allow oil past them under high vacuum conditions, deceleration etc.. Usually not enough to show up on the dipstick till it gets really bad, or till plugs start getting oil fouled. I'd let it go, unless it's a daily driver and you start getting a cloud when you first start it back up after using it.

[t walgamuth]

Agree with above post. Sounds normal to me.