280SL rebuilt engine

[Bill]

Installed a rebuilt(Robt Fenton)280SE short block engine in my ‘67 230SL, Starts  great and performs great but gets terrible gas Milage…i.e..maybe 12 miles per/gal. What’s happening? Installation done by Silver Star Motors in Sacramento,Ca.

[rwmastel]

Was the mechanical fuel pump also rebuilt?

For the less initiated with engine rebuilds, does "short block" mean nothing in the head was rebuilt?  Just worked on everything in the block?

[mdsalemi]

Was the mechanical fuel pump also rebuilt?

For the less initiated with engine rebuilds, does "short block" mean nothing in the head was rebuilt?  Just worked on everything in the block?

A reasonable explanation:
https://www.motortrend.com/how-to/difference-between-long-and-short-blocks/

[rwmastel]

Right, so valve issues may exist that may partially contribute to the poor MPGs.

[Bill]

Yah! Head rebuilt too.  New exhaust valves,springs, etc.. Just went thru the injector pump and installed a new “choke”(whatever it’s called) mechanism plus tuned the pump. Appear to have solved the rich mixture issue. Now getting normal milage and the spark plugs are now clean.,