Tried to run rebuilt 7.4l with muffs on lower unit and can not get water thru exhaust. Took boat to boat ramp, left on trailer, started engine and water thru exhaust fine. I need to be able to run engine at home to complete tuneup. Any suggestions?
If it works in the water it will work on muffs. Those muffs don't seal all that well. you might try getting the type that pumps water in both sides and tie them in place so they do not move. I have had mine slip down when I turn on the water.
