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How to cure backfiring in my 1979 930


Vehicle Information: Year: 1979; Engine (Size, Modifications): 3.3 l stock; Total Mileage: 200,000 km. Engine and fuel system rebuilt at 160,000 km;

Six years ago I purchased a 1979 Canadian model 930 with 130 Km. Since then the engine and fuel system were rebuilt. Currently, I have 200,000 km on the car.Recently, my mechanic replaced the exhaust system with a European free flow system including a Dansk muffler. Now, when I decelerate from 4000-5000 rpm, I experience very loud backfiring (popping sounds) which did not occur with the stock exhaust system. The noise is so loud that I must put in the clutch when I am on city streets. My mechanic has assured me that the mixture and timing is within acceptable factory limits and there are no leaks in the exhaust system. One person suggested that the 79 930s are more prone to backfiring. How can I eliminate or minimize the noise. Would it help to replace the muffler with another brand such as Borla or install a stock muffler?

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