Help with 40 hp 73 Evinrude

[Herman]

" The motor runs great at low

" The motor runs great at low throttle. If I try to speed up, the engine revs but I don't go any faster. Someone suggested the propeller, so I had it serviced for $65 but it didn't solve the problem. Any help would be appreciated? Thanks. "

 

[Herman]

" I wanted to add that it does

" I wanted to add that it doesn't appear to be slipping out of gear. When I throttle back down, everything seems OK again. Also, the gear shifter isn't moving when this happens. Again, thanks for any help. "

 

[josh hildreth]

i would think that it is your

i would think that it is your propeller how did this happen did it happen all of the sudden? or was it sitting? did you get the lower unit serviced recently?

 

[joereeves]

"Herman.... If the engine rpms

"Herman.... If the engine rpms increase and it sounds like the prop is out of the water (the roar of the exhaust gets louder), you may have a problem such as follows:

1 - The boat may have been on a improperly adjusted trailer for a long period, resulting in what is refered to as a hook in the hull (the hull is pushed upwards in the center area). As the boat travels forward, this condition causes the back of the boat to ride high, with the bow down, causing the prop to break the surface and cavitate, ventilate (spin in the air).

2 - The engine is angled too far inwards on the reverse lock rod. Applying throttle in this condition makes the bow plow in, and at the same time makes the back of the boat and the prop raise up out of the water.

3 - You may have a 15" shaft engine on a 20" transom boat. At slow speed, you would have some propulsion, but as your speed increases the back of the boat raises, lifting the lower unit out of the water.

With the boat on the trailer, back away from it and look at it from the side. Sight along the bottom (the keel) of the boat. The cavitation plate (the plate just above the prop) should be on a parallel with the keel, with the cavitation plate being approximately 1" below the keel (but not over that 1"). Let me know what you find.

Joe

"

 

[Herman]

" I haven't had the motor

" I haven't had the motor serviced and it has been running fine before this (earlier this summer, etc.) The boat was sitting in the water for a couple of weeks before this happened. I don't think it is cavitating because it was running fine about a month ago and it does appear to be trying to push the bow up when I increase the throttle. I could add that the same thing happens in reverse.

A spun prop certainly sounds possible, but I guess I thought that it has been fixed. Is there something in the lower unit that would cause this to happen? Is there a way to check the prop? "

 

[chinewalker]

" Another thing to follow up o

" Another thing to follow up on would be the splines in the driveshaft to crankshaft journal. I had a similar 40hp that had the crankshaft splines rusted out. Motor would grip enough at idle to move, but at higher revs it would slip. There's no easy fix for that one.

An easy check would be to remove the little cover on the side of the lower unit and view the driveshaft. Pull the spark plug wires. With the motor in gear, try turning the propeller. If the driveshaft is moving and the flywheel is not, then you may have the worn splines. Or, hold the prop from turning and have someone try to turn the flywheel.

The prevention for this is to always grease the end of the driveshaft when reassembling the lower unit on the motor, and make sure the o-ring is in place.

Scott "

 

[joereeves]

"Herman.... You mention "S

"Herman.... You mention "Sitting in the water" and that made me wonder if you're in a area where barnacles would form, and if so, is the bottom of your boat protected with a "Anti Fouling" paint? I've encountered this problem a few times whereas the bottom was so encrusted that speed of any kind was impossible.

Joe

"

 

[Herman]

" Joe/Scott/Josh.....Thanks fo

" Joe/Scott/Josh.....Thanks for all your help. I will check the splines this weekend as suggested and report back. I don't like the sound of "no easy fix" though. If it turns out to be the splines (whatever they are), I will be back with a big HELP! Thanks again. "