Dear Tom and Ray:

I have an '81 Chevy Caprice and it backfires. What do I have to do to correct this problem? -- Lawrence

Ray: Get a '91 Chevy Caprice.

Tom: Most of the backfiring I've seen on these cars is the type that occurs under the hood, rather than out the tailpipe. So I'm going to assume that's what you've got.

Ray: And it's usually caused by one of two things -- either bad ignition timing (which is often the result of a worn-out timing chain) or, more likely, a weak accelerator pump in the carburetor.

Tom: When the accelerator pump is really weak, the fuel mixture becomes so lean that the flame in the cylinder propogates too quickly ... so quickly that some of it sneaks out the open intake valve. And that popping sound you're hearing is that part of the combustion that's taking place in the intake manifold.

Ray: So check the timing, Lawrence, and if it's OK, then a new accelerator pump or a carburetor rebuild might be in order.

Auto repairs can be costly! Save money by ordering Tom and Ray's pamphlet "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.

© 1998 by Tom and Ray Magliozzi and Doug Berman Distributed by King Features Syndicate, Inc.

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