15 hp evinrude wont stay at full speed

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chrisc54

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Hey everyone, i just finished raising up my transom as too much water was splashing in, but now i am having a problem, the part circled in red in the picture is not getting directly under the water. My motor is still pissing out a good amount of water. But i noticed going ful speed my motor will all the sudden want to slow down a whole bunch, but would still run fine. I was thinking maybe it was starting to overheat going that fast as that part (circled red) is not under water. The motor idles fine, and trolls fine because the circled red part ius under the water until i take off fast...then within 30 seconds full speed wants to go a lot slower.

REally need some advice on this and woulod appreciate it
 

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It is overheating and going into safety mode. It is sucking air if those holes are not under water. You will have to lower your motor.
 
okay thanks! how come it was still shooting water out of the holes though? im sort of a rooky to outboard motors just wondering where the pump intakes the water from basically....thanks
 
I'm pretty new at this but aren't those exhaust holes?

https://www.leeroysramblings.com/water_circulation.htm
 
i believe those are the exhuast holes, but they still have to be underwater to prevent overheating?
 
Bad Wolf said:
I'm pretty new at this but aren't those exhaust holes?

https://www.leeroysramblings.com/water_circulation.htm

yup those are exhaust holes. actually it looks like the motor height is fine. you want the bottom of the boat to be even with the cavitation plate. as for the odd running motor, you may have a spun prop, or try different settings with the tilt pin.

as long as the transom is at the least 15" you should be good to go.

my other boat motor that i raised, this is a bad angle,
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but i raised my motor and i could probably raise it another inch or so.

i think you have a fuel pump problem (bad diaphram) or a spun hub on the prop.

dino
 
Yes I was incorrect about those holes, I still say it is heating and going into slow mode though if it did fine when it was lowered. How old is your pump? If your hub was spinning your motor would still be revving up high, you just wouldn't be moving fast.
 
chrisc54 said:
i believe those are the exhuast holes, but they still have to be underwater to prevent overheating?
They are exhaust holes. They are supposed to be slightly above water while on plane. They only discharge water, its not an intake. Make sure you don't have a leaky head gasket. That happened to me and water was getting into the cylinder causing it to bog down.
 
nccatfisher said:
Yes I was incorrect about those holes, I still say it is heating and going into slow mode though if it did fine when it was lowered. How old is your pump? If your hub was spinning your motor would still be revving up high, you just wouldn't be moving fast.
I don't believe that the 9.9/15 hp of that vintage were equipped with S.L.O.W. None of mine have been
 
BoatingCop said:
nccatfisher said:
Yes I was incorrect about those holes, I still say it is heating and going into slow mode though if it did fine when it was lowered. How old is your pump? If your hub was spinning your motor would still be revving up high, you just wouldn't be moving fast.
I don't believe that the 9.9/15 hp of that vintage were equipped with S.L.O.W. None of mine have been
I didn't catch the year model but after looking at the color of it I would say you are correct. I had a '94 that had it on it but don't know how much earlier they had it on them. I am sure that motor is at least 10 years older than that.
 
That motor is from the 70's and did not have SLOW. Do your RPM's drop as the speed drops or the RPM's stay up and just the speed drops? Could be a problem with prop cavitation or ventilation. Is the surface of the prop smooth or does it feel rough and have pitting? Is that pic of your boat after you raised the transom? I don't see where it was raised. As others have said it has nothing to do with those exhast holes.
 
just to clarify thats not my motor, just a picture of the ssame online that i found..one that i could use as an example, sorry
 
the rpms also went down, and then i would just troll my way in slowly after that would happen, because the motor still idles and ran good until the exhuast holes began to be exposed
 
Does your prop still have the converging ring on it? If not factory, is it flared? Does it sound as if its cavitation? To see if its getting hot, try touching the head. You should be able to leave your hand on it for a few seconds. If you can't touch it at all then it's overheating.
 
okay, so yeah thats not my motor or boat just an example of my motor but an older version. Mine is a 1992, the rpms drop with the speed when it slows. The prop does have a small little ding in one of the prop blades but it never affected it before. When i started my motor for the first time this year it would run and then die in forward...so i brought it home ran seafoam through it and tinkered with the carb settings and it was good. The year before i never had a problem so i assume it was just running out the cobwebs, it only sat for 4 or 5 months, the motor is mainly used in saltwater and then flushed out
 
so i took the lift off of my transom, it is now 15" high and i have a short shaft, (which is proper)?...i had it lifted roughly 4.5 5" higher so much to high for a short shaft, although when idling or going slow it was okay but i think that when i went full speed its possible that even the water pump intake wasnt getting in quiete enough water,. Testing it tomorrow hopefully
 

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