Oil & Fuel Kubota l185dt starting problems

[Pt farmr]

Have just bought l185dt with starting problem and would like ideas on the cause. When I start the tractor the throttle needs to be on full to get it going. It cranks a while and when it starts to fire, belches smoke and runs rough till smooths out and then you can throttle down.Also need to shut off fuel when not in use since it will drain itself. Injector pump is wet at the point of fuel line and vent and lower around 4 bolt square plate. Is there o-rings on the vent screw? Is there another problem to look at? Fuel line is new. New to owning a tractor not sure where to start any advice would help. Thanks