intermittent backfire with loss of power, briefly. under load and driving on flat.

1969 CHEVROLET BEL AIR
140,000 MILES • 2.4L • 6 CYL • 2WD • AUTOMATIC
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JOHNEBOY
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new- points, condenser, rotor , cap, plugs. valve job four months ago with followup re-torque and valve adjust. ran fine til yesterday when intermittent momentary loss of power and backfire started. timing is set at 6 degrees with 2 degrees oscillation so timing chain is good. possible bad coil?
Jan 20, 2015 at 2:59 PM
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HMAC300
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check dist cap for cracks or carbon tracking. check coil for cracks around tower or spray water on coil,wires and cap and see if it makes a difference. check carb for nuts being tight as they used to loosen up as well as float bowl. take air cleaner off and see if top of carb will shake by hand with engine off if it does the float bowl is loose. check for a cracked manifold, both of them. as well as a vacuum leak. make sure wires are on correctly 1-5-3-6-2-4 firing order
Jan 20, 2015 at 3:15 PM
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JOHNEBOY
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will try in the morning and let you know. thanks
Jan 20, 2015 at 7:17 PM
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JOHNEBOY
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HMAC300; replaced cap and rotor (no carbon tracks or cracks), no cracks or loose bolts on manifolds or carb, wires are good, ran my hand along each one while engine was running. Funny thing is the engine quit running twice while doing this.Timing and dwell are within limits. Could the coil be bad? Backfire is in the exhaust almost like I was turning the key off and on.
Jan 21, 2015 at 10:34 AM
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HMAC300
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check your compression it's a good possibility that you have a burnt valve, short each cylinder out one at a time to see if the backfire or spitting goes away. it may be compression leaking through valve making it sound like a backfire. Could also be a head gasket as well.
Jan 21, 2015 at 12:02 PM