slight backfire when downshifting in second gear

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fran kelly
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slight backfire when downshifting in second gear

#1 Post by fran kelly »

Just took my 356C out of storage and drove it less than 100 miles so far. Today I noticed a popping or slight backfire when I downshift to second gear and it doesn't seem to matter what the rpm's are. Several years ago I had a very loud backfire issue when downshifting and it was an exhaust manifold gasket. This is nowhere near that but I am wondering what people may think is the problem. No performance issues with acceleration - just this new noise. Possible air/mixture issue with the Webers?

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VinceFinaldi
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Re: slight backfire when downshifting in second gear

#2 Post by VinceFinaldi »

That popping is usually when unspent fuel ignites in the exhaust...not a true backfire. In order to do that it needs oxygen. Thus, when you have an exhaust leak (bad gasket, cracks) it introduces oxygen and boom. Classic example is a bad air check valve on early cars w smog equipment. Check the exhaust first. If that's not it, then it could be a carb issue (too much gas getting in on decel)

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