I am stumped....... I have completed the following repair/replacments and still cannot get over 4000 RPM?<br />Waterpump/impeller<br />Fuel pump<br />carbs cleaned and sync<br />Compresion is 125,125,130<br />spark on all cyl<br />15 pitch prop<br /><br />Could it be the Tach? I have a 18ft...