There is an adjustment. The 50-175 Service Manual available for download from this site says: When the carburetor adjustment has been made, the oil pump control should be checked and adjusted. With the throttle completely closed, the oil pump outer
cable should have 1/16 of an inch of free play at the oil pump cable stop before it moves the control arm
on the pump from the stop pin. Adjustment is made by the cable adjuster located in the cable by the
transmission oil filter plug.
A fouling spark plug may indicate that the spark is too weak. The contact point surfaces may need to be cleaned up. You should be able to get at least 1/8" spark kicking it through.
Hope that helps.