On the Cobra drive, the impeller is easy to replace (probably the easiest there is) but there are a few tricks:
1)replace the wear plate if its even a little scored
2)when you re-install the plastic impeller housing, make sure that you get the o ring gasket in the groove. although the shop manual says to use OMC gasket sealer on the oring gasket, I found that it stays in place better and seals just as well if you use a thick grease like OMC triple guard grease.
3)When running it on the water hose, leave the plastic cover off the rear of the upper gear housing, make sure that: water shoots out of the little rubber hose fitting on the impeller housing, this helps it prime
4)make sure there are no water leaks round the plastic housing, that is a sign of an improperly installed o ring gasket.
if when you removed your old impeller, there were pieces of the fins missing, then you need to clean out the raw water intake hose and thermostat housing, that is where they can get trapped and block water flow....
