WARNING!  It has been many years since I read this procedure.  My recollection may be faulty and changing a fuel injection setting is risky.  The actual procedure is on the internet somewhere. 

There is a small plate on the side of the fuel injection pump held on with 2 screws.  Take that off and turn the engine over until a screw with a locknut is visible in the hole.  I do not remember if you screw that in or out to increase the fuel.  I do remember that a small change goes a long way.  I would not change it more than 1/3 of a turn without a test run.