2015 F115LB overspeed

[Seabags6016]

I bough a new G3 pontoon boat in 2015 with a F115LB engine. Used it got approximately 200 hours on it. WOT was at 6000 RPM. Now one day last week it was at 6800 - 7000 RPM when I noticed it. Bought back the throttle an inch off the stop to where it ran at 5500 rpm. It continues to go high when pushed against the stop. Sounds the same at WOT. Yamaha said its under propped. Hard to believe that all of a sudden its under propped. Any ideas or suggestions before I start playing with props? If it is an indication problem, what would be the cause? If actual overspeed, computer bad??

[pstephens46]

Who at Yamaha said that? Is it a Faria guage?

[fairdeal]

Now one day last week it was at 6800 - 7000 RPM when I noticed it. ...
Yamaha said its under propped.

I would have thought "Yamaha" would tell you,
that its impossible to exceed 6450 rpm
because the ECM cuts off ignition and fuel injection then

as pstephens asks - what are you getting your RPM info from ?
has that changed?

[99yam40]

checking the RPM with another gauge would be the proper thing to do before changing props

does this rig include a jack plate and did you have it raised too high?
or did you have the trim set too high ?

[Seabags6016]

Yes it is a Faria gauge that came with the boat. Just one day it started to go to 7K. I don't know a lot about outboard motors but assume there must be a pick up somewhere to give me the speed indication.

[Seabags6016]

I was on what I thought was a Yamaha site and here's their reply;

Hello Mike,

The engine is not propped properly; the propeller is too small and causing the engine to over-rev. And yes, this will cause a problem. It could destroy the engine.
We suggest you prop the engine to 5600-5800 rpm max. When the boat is loaded it will go to 5000 rpm and when it is not it will go to around 6000 rpm.

Regards,

Diane

I replied back saying it just started. If it was new I can see that. Havent answered back.

[fairdeal]

Yes it is a Faria gauge that came with the boat. Just one day it started to go to 7K.

So it a problem with the Faria gauge - the rpms you are seeing are incorrectly indicated.

As stated above, the engine ECM simply will not allow it to rev higher than 6450 rpm



Can you share with us the url of the site where "Diane" provides her guidance?