W116 only 1/2 throttle

[cdnturbo]

My son just bought a 1978 280 se  When accelerating he only gets half throttle.  The peddle does go all the way to the floor but the motor does not rev fully. If we go under the hood and manually rev the motor it does much better. Is there an adjustment we can try?

[ZCarFan]

You need to have someone operate the pedal and watch the linkage.  If you are missing that much travel, the cause should be easy to spot.  There are adjustments, but first you need to assess what is actually wrong first before trying that.

[oversize]

Check the linkage at the firewall