Last winter I took off the lower unit on my 15 hp Honda and replaced the drive shaft and prop shaft. I put it all back together and every thing seemed fine until I noticed that at high RPM it doesn't move water through the cooling system. It will slow down until nothing but steam comes out. If I stop it will start circulating again. It seems to have less water moving through it at all speeds also. Any Ideas? I ran it for about 1 1/2 hours on sunday and by the end of the run it seemed to be doing better, but I am going to take it on a trip next weekend and want ever thing in top shape.