Question: 496HO, tach reading way high?

[Teabagger]

Just took out my new boat for the first time and the tach is reading super high seems like double what it likely should be. My builder is closed until Tuesday and I don't really care to haul it back up there so I hope to find an answer here and fix it myself, anyone have any idea's as to what I should look for to troubleshoot?

[THOR]

Just took out my new boat for the first time and the tach is reading super high seems like double what it likely should be. My builder is closed until Tuesday and I don't really care to haul it back up there so I hope to find an answer here and fix it myself, anyone have any idea's as to what I should look for to troubleshoot?
Some tachs or sending units have a setting for 8,6, or 4 cylinders. If you have one of these then and it is set on the wrong setting then it stands to reason as to why you seem high.

[riverroyal]

infooooo

[SnakeWrench]

What rpm is it reading and what's it reading at idle. More info please.

[JB in so cal]

I'm gonna go out on a limb, here: I'd say more info is needed.

[phebus]

Like Thor said, most tachs have a selector switch on the back that lets you select 4, 6, or 8 cylinders. Check to see if it is in the right position (sounds like it is set on 4). If it is set to 8, go through it's settings a couple of times, the contacts might be dirty, and a little scrubbing is needed.
I have had this problem before.

[SummitKarl]

check for loose spark plug wire first
then check the "cyl" selector switch on the back of the tach

[Teabagger]

It's a 496HO. Tach is a Beede unit, it's reading about double. Idle is roughly 1100ish rpm when it should be 650ish. Half throttle went too 6000rpm if I remember the reading correctly, but motor wasn't even turning close to that, just running along quietly and gps speedo was reading 35 mph. Looks like I'll have to check the back for that switch (although I don't remember seeing one but I didn't look too hard) unless anyone has other idea's on what to check.
I was thinking it may need a tach adapter or something that was missed during the build? Hopefully it's just a simple switch...

[phebus]

Look good, you'll find it. It may be recessed, so look for a hole in the back, and the cyl. numbers might be cast into the plastic and hard to see. My tach is a Beede also.

[Teabagger]

phebus,
Thank you very much!