Dear Tom & Ray:

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.