1972 Johnson 40hp does same speed at half and full throttle

[hooter85742]

I have a 1972 johnson 40hp model 40R72E. The boat is a 14 foot 7 inch Arrow Glass model the Scorpin. I think its a around about but I look it as a ski boat. I have went throw and have the motor sound. At half or full throttle it does the small speed in the water. I do not have an electric tilt. I have to pull a pin to change the position of the motor. It has what I call a whale tail added to it. The prop is a 10 and something inch 3 blades with a pointed cone at the end. A pin holds the prop to the shaft and a key holds the cone on and hold the pin in place. I think its the prop but, then I am new to boats. I can tell the RPM's raise alot. I pulled the lower unit apart and everthing was nice and tight. The gears and splines looked really good. Can someone help me out. Is there a way to see if the prop is bad. Or is there a way to put a newer style prop on it. the old style I can get one for around $125. But it looks like a fan blade from the 1920's LOL. In changing the tilt of the motor I did find that when the pin is at the closest point to the hual the nose of the boat was way up in the air. when out away from the hual the nose was not up in the air as much. the point that the owner before me used was okay but no speed and it would not get on plain. Going slow and working up to a higher speed did not help once at one speed thats it it will not go fast but the motor has lots more to give. Its like spinning my wheels in the mud lots of noise but I get nowhere.

One other thing What fluid can I use in the lower unit. Is it like gear oil, motor oil, transmission fluid? The closest Johnson dealer is 50 miles from me. So if Walmart has something that will work in place of the factory stuff I would rather save myself a long drive. Thanks everone.. Hubert

 

[F_R]

Re: 1972 Johnson 40hp does same speed at half and full throttle

80-90 weight outboard gear oil from Wal Mart.

I'll bet your prop hub is slipping. Make a mark on the plastic prop cone, and another on the propeller itself, aligned with the first one. Then run the motor till you experience the suspected slipping. Stop the motor and check the marks. If no longer aligned, the hub slipped. Get the prop re-hubbed or buy a new one.

Another possibility is cavitation from that whale tail. Try removing it to see.

Too bad you tore it all apart for a bad prop hub.

 

[hooter85742]

Re: 1972 Johnson 40hp does same speed at half and full throttle

Thank You, I had no clue that inside the prop it was rubber. I was thinking it was like a metal spline on spline. Your picture sure looks like the prop I have. I am looking for more information on the motor. I guess I will have to buy a book. to figure out the other issues. Like its not charging, will not shut off with the key. I think parts are missing like the likk switch. Parts of the electric choke. It has no gauges at all. I would love to have a RPM gauge. I added a voltmeter today along with a stereo and a few lights. Driving lights, a blue and purple neon along with white lights inside. But its all usless till I get the battery charging. Then I may add an amp and big speakers.My mom thinks I turn the radio up cuz I like music, most of the time its just so I can not hear her back seat driving LOL.