The case of the backfiring MG.

Dear Car Talk

Dear Car Talk | May 01, 1993

Dear Tom and Ray:

I drive a 1973 MGB (yes, every day). When I ease off the accelerator at 55-60 mph, like when I'm going downhill, the car does an almost constant series of small backfires until I accelerate again. The problem seems to be worse before the car is fully warmed up. Could this have anything to do with the fact that the exhaust system is held together only by rust and baling wire?

RAY: Sounds like it's in perfect running order to me, Rose. Every MG I've ever seen runs just like this!

TOM: I apologize for my insensitive brother, Rose. He has no place in his heart for romantic cars like MGs.

RAY: Romantic? There's no ROOM for anything romantic in an MG!

TOM: Your problem may very well be related to your exhaust system, Rose. If there are lots of holes in it, and it's not creating enough "back pressure," then the combustion gasses can come out of the cylinders too fast. When that happens, they explode "further down the line" in the exhaust system. That's what a backfire is.

RAY: If you're lucky, one of these backfires will be big enough to blow the exhaust system off entirely. Then you'll have to get a new one and your problem will be solved.

TOM: But before you set out to blow off the exhaust system, have your mechanic check for a few other things. Make sure the choke isn't sticking, that the mixture isn't too rich, and that the timing isn't too advanced. Any of those could also contribute to a backfiring problem. Good luck, Rose.

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