1986 Aspencade SEI

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That's great!! BUT...if you have an '86 SEi you don't have carbs...it is Fuel Injected. You can synch the throttlebodies. The backfire seems to me like maybe an injector is a little dirty. Try some Seafoam in the tank to clean things up. Other than that it may be a very small vacuum leak. The backfire is a lean condition (too much air to gas ratio causing a "pre-ignition" during no-load conditions). Could also be a spark plug that is misfiring. Pull the plugs to check them. If you have the manual...check the troubleshooting section.

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Kim I had an 86 se-i & mine did the same thing only it sounded like a gun fire turns out the black o-rings about the size of a 50 cent piece were all faulty they went between the trottle boddies & the intake manifolds !

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Kim: Had the backfiring problem on my 85 limited,both during de-cel and downshifting. Pull your air box out and check the vacuum hoses that are aft of the box. Also check the hoses on the 2 T fittings. I had 2 hoses off. I replaced the hoses, changed the airfilter (while I was in there) and wa--------la, problem solved. Like they say on this fantastic forum, "check the easy things first!!"