I have a 1989 yamaha 15hp. It ran good for 6 years and all of a sudden it got to where it is hard to start and once it does start it will idle at high rpms, but when I cut it down to low idle it dies. I checked the compression which was 120 in each cylinder. I rebuilt the carb and cleaned it VERY good, set the float hieght and tuned it to the specs in my manual. I put a new CDI unit and ignition coil on it. changed plugs and set to correct gap, changed the gas also. It' still hard to start and dies at low idle. I noticed that my exaust cover gasket and head gasket were really corroded and water has been leaking into the lower cowling were the powerhead sits. Could water be getting into the powerhead and cause hard starting and to die at low idle? Thanks