i have a OMC Cobra 5.8 when i put the water muffs on with semi forced water it does not get to the impeller, i replaced the impeller and still no water, i checked thermostat, could there be a blockage? and where would i start to determine that,i have the seloc online manual but theres no troubleshooting guide for this problem, thought about dropping lower unit and starting there.any help would would be greatful