Topic: 1959 Evinrude 18HP has power, moves water but….

This topic has 22 replies, 9 voices, and was last updated 7 years, 11 months ago by harpua.

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May 2, 2017 at 12:17 am #6897
harpua
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had her out on the lake today. starts up beautifully but when i give her full throttle it feels like she is slipping and revving really high, maybe sputtering a bit. from 0-6.5 MPH she is great, then about 6.7 she starts to rev high and i pull back throttle.

I changed all the internal fuel lines to 3/16 which i think may be too big. wondering if air getting in the carb from unsealed hoses or a larger hose size would give this result. and if not, what would give this result?

thanks
May 2, 2017 at 12:37 am #56965
RICK EICHRODT
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Lifetime Member
Sounds like a slipping prop hub….spun hub would cause it to rev up and not push the boat up on top.
May 2, 2017 at 12:38 am #56966
frankr
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Revving and slipping is a classic symptom of a slipping propeller hub. To test, make a mark on the prop nut (or use the cotter pin as a mark).
Then make a mark on the propeller, aligned with the first mark. Run the motor till suspected slippage occurs. Stop motor and check the marks.
If they are no longer aligned, the hub slipped. The cure is replace the prop. Or the old one can be repaired, but probably isn’t worth the cost.

BTW, it isn’t the fuel lines.

EDIT: Posted the same time as rick
May 2, 2017 at 10:51 am #56982
harpua
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thank you both very much. the engine seems pretty strong otherwise. what year range will fit on my 59? will all the way up to 68 work?

are props for these hard to come by?

also can anyone tell me if 3/16 fuel line hose under the cowl is ok? seems it would be fine if this is the case.
May 2, 2017 at 12:00 pm #56984
aquasonic
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US Member
quote FrankR:

BTW, it isn’t the fuel lines.

3/16" fuel line always works for me.
May 2, 2017 at 12:30 pm #56987
frankr
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quote Harpua:

thank you both very much. the engine seems pretty strong otherwise. what year range will fit on my 59? will all the way up to 68 work?

are props for these hard to come by?

As far as fitting the motor, any of the 18-20hp years will work as long as it is pin drive (not splined). Of course there are a number of different diameters & pitches, materials and shapes. All in the search for the perfect prop which hasn’t been invented yet.
May 2, 2017 at 1:05 pm #56988
harpua
Participant
quote FrankR:

quote Harpua:

thank you both very much. the engine seems pretty strong otherwise. what year range will fit on my 59? will all the way up to 68 work?

are props for these hard to come by?

As far as fitting the motor, any of the 18-20hp years will work as long as it is pin drive (not splined). Of course there are a number of different diameters & pitches, materials and shapes. All in the search for the perfect prop which hasn’t been invented yet.

ah, got it, thanks. my 9.9 sits much lower in the water than this motor. i am wondering if cavitation is something i should consider. and then youre going to tell me something like "its not that" – and i am going to feel better. sort of, and check the prop out, right?

😀
May 2, 2017 at 1:41 pm #56990
fisherman6
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US Member
Hmmmm, You say your 9.9 sits much lower in the water. Is your 9.9 a long shaft motor? Is it possible you have a 20" transom on your boat? The "short shaft" 18s of this era have a shaft length of about 18". Kind of a "mid length" shaft and would be too short for a long shaft transom. If that is the situation, cavitation could most definitely be your problem. Maybe just as the boat begins to plane it’s lifting the prop too close to the surface and it cavitation. The anti cavitation plate should be nearly even with the bottom of the boat when mounted to the transom. Say +/- about 1".

Measure your boat’s transom. If it measures very close to 20" from top to bottom and your 18hp doesn’t have the long shaft spacer in the tower, I think we found your problem. If your transomom measures close to 15", then I suspect the prop is spun.
-Ben

OldJohnnyRude on YouTube
May 2, 2017 at 1:59 pm #56992
harpua
Participant
quote Fisherman6:

Hmmmm, You say your 9.9 sits much lower in the water. Is your 9.9 a long shaft motor? Is it possible you have a 20″ transom on your boat? The “short shaft” 18s of this era have a shaft length of about 18″. Kind of a “mid length” shaft and would be too short for a long shaft transom. If that is the situation, cavitation could most definitely be your problem. Maybe just as the boat begins to plane it’s lifting the prop too close to the surface and it cavitation. The anti cavitation plate should be nearly even with the bottom of the boat when mounted to the transom. Say +/- about 1″.

Measure your boat’s transom. If it measures very close to 20″ from top to bottom and your 18hp doesn’t have the long shaft spacer in the tower, I think we found your problem. If your transomom measures close to 15″, then I suspect the prop is spun.
-Ben

Thank you very much Ben. I quickly measured 20.5" from the mounting plate to center of the bottom of the transom. the anti-cavitation plate sits about what looks like 3" maybe from the top?

what can i do to insure this is the case? if i set up a brum and run the engine without load can i figure it out?

Also, if this is the case, i am wondering what the tower spacer is, how its implemented and how i can find one? thanks again.
May 2, 2017 at 2:01 pm #56993
chinewalker
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US Member
Well THERE’S your problem! You need a long shaft extension kit for your 18. You’re ventilating the prop once the water breaks from the transom. Ventilation is NOT the same as cavitation. I’m pretty sure I have the extension housing and possibly some of the other bits, too.
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