Loss of power

I have a 76 Cadillac superior regal hearse for a parts car and was debating if I should pull the motor to keep. After you drive it about 50 miles it loses power. You can press the gas pedal and it does nothing, if you let it coast a minute it will pick backup and go. This will continue until you shut it off and let it sit for a while. After it sits for a few hours its good to go another 50 miles. It has a new carb, radiator, and complete tuneup. Anybody have any ideas as to what could cause it and should I save the motor it only has 65,000 miles?
Thanks
Chris

Check the CAT, or the Y pipe at the exhaust. The cat may be plugged, and the Y pipe has had a problem with the inner sleeve collapsing, causing an obstruction. The Y pipe will not look crushed, as the inner sleeve collapses due to a hot exhaust Y pipe going through a puddle of water.

Or, the motor was run low on oil, and its shot. Check the oil pressure with a manual gauge. Drive it til it does it again, and check the PSI

Chris Elzie said:

I have a 76 Cadillac superior regal hearse for a parts car and was debating if I should pull the motor to keep. After you drive it about 50 miles it loses power. You can press the gas pedal and it does nothing, if you let it coast a minute it will pick backup and go. This will continue until you shut it off and let it sit for a while. After it sits for a few hours its good to go another 50 miles. It has a new carb, radiator, and complete tuneup. Anybody have any ideas as to what could cause it and should I save the motor it only has 65,000 miles?
Thanks
Chris

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Had this issue years ago. My issue was a cracked intake manifold / rotted gaskets. Mine would run like hell until it came up to operating temperature then it would start loosing power and at times no throttle response. However this was with a 472. The crack was caused by water freezing under the manifold after the engine had been washed and left outside in below 32 deg weather. The rotted gaskets are just from not being ran much.

Also check your fuel pump, if it has the stock mechanical one it can cause some strange issues when the diaphragm is starting to go from rot or has a small tear in it that is much more prominent when its warm. This also causes no throttle but will idle with not much issue. Very very common as I have had this issue to many times to count from low mileage coaches.

Fuel pump is the cheaper fix / issue to diagnose with an electric fuel pump.

Hope this helps.

It had the cats taken off and dual exhaust put on so I don't think is that. Now that you mention I remember seeing another car do the same when the oil pump was starting to fail, so I guess I will need to check that. Thank Russ

not this has never worked for me but they tell it it can. take the gas cap of and see. if the vent system is plugged it will form a vacuum and bring it to a halt you let it sit and air sucks in and away you go.