2003 Islandi 250 Opti Won’t Spool up completely

[MightyViking]

The tach doesn’t work on the boat but she is not reaching full revs. Struggles to get on plane and isn’t nearly s fast as she was. I changed spark plugs in my initial attempt to sort it out. What else should I look at? TIA

 

[MightyViking]

Bump

 

[Tim75]

Start with a compression check. All plugs out, WOT. Are you sure all plugs are firing? (Is each plug warm/hot?)

Since the tach is sort of a diagnostic tool, can it get replaced? RPM is an important data point.