i have a 1994 ski nautique with a 351 just got boat running. was setting sence 2006 po left out side all this time uncovered. engine is a 1978 going by numbers. got out on the water when you put it in forward gear rpms drop 800 rpms. idle adjustment wont hold. keeps changing everytime you idle in neutral. had carb rebuilt checked alinement. replace carb and spacer gaskets. im thinking vaccum leak but dont know where else to look any info would gladly be appreceated.