i have a faria tach on my pontoon boat which has a 1998 50 hp johnson out board motor on it. my problem is the tach is stuck on 2100 rpms. i ckecked the back of the tach and found a dirt dobber clod on the terminals and wiring. so i removed the tach and wiring to clean it up but the tach with it disconnected and removed is still stuck on 1200 rpms. whats going on, and is it spose to be like that?