Hey! I was wondering if a 67 Mustang with a 289 engine would need a higher octane gas? I was also wondering the average mpg a 67 mustang with a 289 gets? If you know either answer please reply. Thank you.

 

Unless it's a solid lifter K code engine it will run on 87 octane.

The only thing I'd concern myself with is the engine from the 60's require lead. Since we have no lead in fuel anymore. Either add it as an additive, replace the cylinder heads with 5L heads or cross your fingers that the valve seats don't sink.

 

check for blockage, these shouldn't have a problem.. you say it goes on the floor, then you need a new rubber line that goes between the filler and the tank.. this is a easy fix, open the trunk and undo the clamps that hold it on and remove and inspect it..