I have an '85 Ford Ranger with a problem. Often in temperatures below 50 degrees, usually when there's moisture present, my truck will begin to run rough. It loses power, like it's not running on all cylinders, black smoke comes out the tailpipe, and it sometimes stalls. It usually runs fine until about 35-40 minutes into a highway trip. In warmer weather, there's no problem. My mechanic has said the carburetor is OK. He's replaced the EGR valve, the throttle positioning sensor, plugs, plug wires, rotor and distributor cap. None of that helped. A friend of mine mentioned carburetor icing. Is that possible? -- Harry

Ray: Not only is it possible, Harry. It's extremely likely. In fact, I'll bet my brother's salary on it.

Tom: There's something called the "nozzle effect," which says that when things pass through a nozzle, they cool down. You may wonder why this happens. So do we. Only Bernoulli understands it.

Ray: But we know it does happen in all carburetors. And as the cool, wet air passes through the throat of your carburetor at high speed, it cools off. And when it cools off, it freezes. And when it freezes, it blocks new air from getting through (it looks kind of like my brother trying to swallow one of my mother's meatballs).

Tom: That's why your car runs lousy and black smoke comes out of your tailpipe (black smoke indicates fuel-rich conditions, i.e., too much gas, not enough air).

Ray: And eventually, as I'm sure you know, so much ice builds up that the truck won't run at all -- until you stop, let the heat of the engine melt the ice in the carburetor -- and start up again.

Tom: So what can you do about this problem, Harry? Well, you could move to Honolulu, where there's never been a case of carburetor icing reported to the CDC (the Center for Dying Carburetors).

Ray: My second choice would be to reattach or replace a little paper hose that probably fell off your truck last year. That hose is there to prevent carburetor icing.

Tom: That hose carries warm air from around the exhaust manifold right to the carburetor. And aside from helping your engine run more efficiently in cold weather, because it prevents the gasoline from condensing back into a liquid, it also prevents carburetor icing. That should do it, Harry.

It's amazing how many bad driving habits and wacko theories have been passed down from generation to generation! Tom and Ray set the record straight in their booklet "Ten Ways You May Be Ruining Your Car Without Even Knowing It!" To order, send (check or money order) to Ruin, P.O. Box 536475, Orlando, FL 32853-6475. You can also order online.

© 1996 by Tom and Ray Magliozzi and Doug Berman Distributed by King Features Syndicate, Inc.

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