Have a chance to buy a JD330 with a Yanmar 3tn664j motor,T500 injection pump. The engine runs rough and has a miss on no.1 cyl. When I loosen the no 1 injection line when the engine is not running, the electric pump will run fuel out the fitting on the injection pump like it was straight thru. The other two cylinders run perfect. Is there a small valve in the top of the pump that can be replaced reasonably cheap to fix this or is this a injection pump rebuild? Anyone worked on one of these or have a shop manual?