Top speed with 18hp Evinrude on 14′ aluminum
This topic contains 105 replies, has 22 voices, and was last updated by stephenspann27 2 years ago.
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I think this powerhead had fairly low hours on it, the cross hatching in the bores is still there. Something lead to ti’s desmise, overheating or lack of lubrication. The thermostat was missing when I got the motor. Might be a clue..
When you remove the thermostat, the water follows the path of least resistance. This means most water bypasses the water jacket making the outlet feel very cool. The motor however, is usually getting less and running very hot.. . 🙄
quote Garry in Tampa:When you remove the thermostat, the water follows the path of least resistance. This means most water bypasses the water jacket making the outlet feel very cool. The motor however, is usually getting less and running very hot.. . 🙄
Agreed, and the water flow through too fast to really draw out much heat. I put a thermostat in it before I ran it.
Smaller motors such as a 6 and 9.9-15 are the opposite and will run too cold without a stat and start fouling spark plugs.
I wish I had a good test tank where I could put a load on the motor and watch it with a infrared gun.
Garry,
Thank you so much for the tip on the stat, I own a 58 18hp Johnson & I like it very much!
JeffOne word of warning Stephan, do not try to run at speed in a barrel or garbage can. Idle only with a couple quick jabs of throttle. Get your motor to where it will stay running in the barrel but do your tuning on the lake under load. Adjust high speed first. Then go back and re tweak the idle. Good luck with the new powerhead.
Jeff
I’m able to get 19mph now with a new to me powerhead from wannabee.
How steep is the prop on this motor? Numbers should be under the prop nut.
quote Mumbles:How steep is the prop on this motor? Numbers should be under the prop nut.Prop is 9×10. I’m getting about 4,300RPM. Max HP is 4,500rpm according to the cowl, but operating range is up to 5k.
OK – file the back side only of the leading edge of the propeller to bring it to a knife edge. Make sure all blades are the same to keep it in balance. Cut a yardstick into three pieces and stack them between the motor and transom. Make sure the motor is securely clamped, then check the speed. If it ventilates on turns. take one piece out. . . 😉
\good idea on the yard sticks
The prop is 9” diameter and 10” pitch. I’d like to prop it down a bit to handle more weight. I removed about 150lbs of weight from the boat and went from 15mph to 19mph. I think it was a difference of about 400RPM. Should I go down to a 9×9 or try a 9.25×7? I’m running about 4,450RPM in "light form and about 4k, to 4,100RPM in semi loaded form. Max hp is at 4,500 RPM, but max RPM is 5,0000.
Bump…
Stephen,
I have run about 6 different 18’s over the past 45 years. I have run most of those hours with a 9 X 9 prop and a few with a 9 X 10. All on 14 foot aluminum boats except for some use on a plywood 14 footer.Unless you have a real light boat with a light load, I think you will be much happier with the 9 X 9.
The 18 is no racer but will go fast enough for what it was designed for. They don’t seem to like being overpropped.
JMHO.
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