# Merc 15 too high RPMs? Overheating?



## Creek Runner (Sep 1, 2011)

That motor does not have a protection mode, your prop is slipping causing your engine to rev higher becuase it's not pushing you forward. Keep playing with your set up, also check your hub.

When I say it doesn't have a protection mode I mean there is no slow, or guardian protection. It does have a rev limiter which you may be hitting but that your set up or hub.


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## Dillusion (May 21, 2012)

Right, so in theory something as simple as lowing the jack plate by and inch could fix the issue of slipping?


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## Dillusion (May 21, 2012)

Tested again today, dropped it 1"-1.25" from previous setting and it works like a charm. No more spinning.

When some weeds build up though it causes an air pocket which allows it to spin again making the RPM's shoot up.


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## el9surf (Dec 23, 2008)

Mattyvac,
Are you in the Orlando area? Send me a pm if you live in the area. I would like to check out your boat with the jackplate setup.


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## Guest (Sep 24, 2012)

> Tested again today, dropped it 1"-1.25" from previous setting and it works like a charm. No more spinning.
> 
> When some weeds build up though it causes an air pocket which allows it to spin again making the RPM's shoot up.



Your motor has the water inlet on the bottom of the cavitation plate and not on the lower unit. Not the best motor for a tunnel and a jack plate.

I would take the motor off the jack plate and hang it on the transom and it should stop sucking as much air.


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## Dillusion (May 21, 2012)

> > Tested again today, dropped it 1"-1.25" from previous setting and it works like a charm. No more spinning.
> >
> > When some weeds build up though it causes an air pocket which allows it to spin again making the RPM's shoot up.
> 
> ...


It was pissing fine at the highest setting on the jack plate. I know where the water inlet is and what it looks like when it's sucking up too much air (I did it on the old gheenoe with JP).

It's not ideal, but it works fine.


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## AfterHours2 (Aug 2, 2010)

Eventually, I would measure the foot print of an atlas micro jacker and go from there. Being able to adjust on the fly is a great thing on tunnels. For the most part hanging the motor, shimmed upon the transon, is probably the best thing for now. Your set back is not helping you at all. Other than the plate looks cool on the back...


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## Dillusion (May 21, 2012)

I'm getting an aftermarket cav plate soon so I will be doing more screwing around.


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## AfterHours2 (Aug 2, 2010)

Was just pondering, an Atlas, 25 two stroke with a cupped 4 blade would be the hotness on your Shadowcast. That thing would run super skinny. I don't have your same rig but if you want to test out the motor setup hit me up..


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