Tach "wanders"

[ARCWINSTON]

Hello all,
I have a Faria tach that wanders about 500-700 rpm's at full throttle. My engine is a Yamaha F115 and I normally run 5800 at WOT. When the tach wanders up to 6400-6500 (it never wanders down) there is no audible rise in engine revs or increase/decrease in speed nor does any rev limiter kick in. The prop hub is not spun. The connections on the tach are sound. The problem is intermittent and random the only consistent thing being that it happens at WOT.
Is the problem most likely in the tach itself? All comments appreciated. Thanks...W

 

[Texasmark]

Re: Tach "wanders"

We just replaced the wandering tach on the son's Merc. It could have been the trigger source coming from the voltage regulators but since there are two separate regulators and two possible tach drives, substitution revealed that the regulator was not the issue.

Replacing the tach corrected the problem.

Mark

 

[drewpster]

Re: Tach "wanders"

Being that the problem happens only in the higher range of the Tach I am inclined to believe it is the tach itself.