Classic Thunderbird Backfire
A friend's 55 T-Bird with the 292/Fordomatic is backfiring into the exhaust pipe. It sounds like loud popcorn popping on the left side only. The top end has been freshened recently, compression averages 130 with none lower than 120. The carb has been rebuilt and an electronic module replaced the points. Timing is set to factory specs. The vacuum advance diaphragm is good, checked this morning by plugging the diaphragm port and trying to move the point plate. Also checked the other way by moving the plate, blocking the diaphragm, and seeing the plate not move until the port was open. We bled propane around any possible vacuum or air leak location with no change in engine note. Now it idles ok with a little popping but it will really bang when the throttle is opened and when the engine is turned off. It sounds like the exhaust valves are staying open during the compression and firing and burning (detonating) the extra gas in the pipes. Any ideas will be appreciated.
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"Do Not Go Gentle Into That Good Night"
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Plug wires not properly indexed in the distributor cap (one cylinder firing with the exhaust valve open)?
If it runs better when cold than warmed up , one or more exhaust valves clearance might be set to tight.
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