Tach reading almost 3000 rpm at idle before dropping

badrano

Petty Officer 1st Class
Joined
Aug 7, 2018
Messages
331
Got home with the boat and fired it up to flush it out. Tach jumped to almost 3000 as it started up and then dropped to around 1000 after a few seconds. The engine was at high idle with TKS hissing away

Any ideas of why the tach would read almost 3000 rpm when the engine is at idle then drop off to around 1000?
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
These tachos are 'unsprung', meaning they will wander to any place they like (rarely zero) when there's not enough voltage to drive them properly. My tacho will bounce around the 4,000 to 6,000 (and beyond) if the battery voltage drops while cranking...

What you're seeing is perfectly normal...

Chris.....
 
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