Since car type is not mentioned, we [ I ] can only guess. Mention of vacuum line is a clue. Guessing the vacuum controller is bad and not changing as it should. Happened on my '92 Roadmaster. Controller from a junk yard Caprice worked.
Raul, that is a 263 for certain. All 1950 Specials were 248. The last ones. Actually a one year engine.
See the water pump outlet coming around into the side of the block? 1950 and later.
See the "ribs" on the cylinders? 263 only. Post war [ 1946 and later ] engines had the series number...
From what I can see in the driver side picture, I believe you have a 1953 engine, which is a 263. The air cleaner on earlier engines set
square" with the engine, not angled forward as yours. Did that in 53 only. Of course, valve cover may not be original. It IS a '50 or later as evidenced by...
Jer, thanks for joining us. That is not an original number. Been ground off and restamped. Some more pictures of the engine might help. Drivers side down low. I believe the engine number is stamped under the water pump as well. Is in '50s any way.
Bob has confirmed a 263 engine. Pictures of the driver side would further confirm.
I warmed up a '51 263 for my 1950 Special. Not cheap, but WAY more satisfying than any swap. I did after market pistons to increase the compression to 9.5/1. Bored out to 85 MM. Had the head...