1954 Evinrude sounding bad at full throttle

[Yadrif]

Hello Everyone,
I have a 1954 Evinrude Fleetwin 7.5 hp. It runs good at low to medium throttle but when ran at full throttle it seems to just rev up without getting any more speed.

Does anyone have any suggestions for things to look at for this issue?

If you need more infomation please let me know and I'll get it.

Thanks for the help.

 

[jbjennings]

Re: 1954 Evinrude sounding bad at full throttle

Sounds like you might have a spun prop.

 

[F_R]

Re: 1954 Evinrude sounding bad at full throttle

Good generic suggestion, but not if it is the original type prop. They didn't have a rubber hub. But what they do have is a "shock absorber" in the lower unit. The shock absorber has a heavy spring inside that is noted for breaking. Usually, when they break it locks up the lower unit, but not always. Sometimes they just slip.

If it were a broken drive (shear) pin it wouldn't go at all. But you DID check it, right?

 

[Yadrif]

Re: 1954 Evinrude sounding bad at full throttle

Thanks for the advice.

I removed the prop and there is no rubber hub. Also, the shear pin is not broken.

How do I inspect the shock absorber?

If it is real involved I'll purchase a repair manual but it would be great to check this before I can get the manual.

Thanks.

 

[F_R]

Re: 1954 Evinrude sounding bad at full throttle

First you have to remove the powerhead to access and disconnect the shift linkage.

Then you remove the lower unit

Then you remove the water pump

Then you remove the bearing housing below the water pump

Then you pull the shock absorber out of the gearcase.

Testing it is another matter. Kind of difficult to apply the torque required. If you clean out the inside real good, you can look down in there and sometimes see if the spring is broken. Usually when it breaks the increased length burns the bottom of the bearing plate. Also, if it pulls apart real easy there is a problem. It should be very difficult to get it apart and you should not even try.

 

[cc67]

Re: 1954 Evinrude sounding bad at full throttle

Just a thought, but I assume you are running it on a boat made for a short shaft motor (15" transom).

 

[Yadrif]

Re: 1954 Evinrude sounding bad at full throttle

Thanks for the suggestion.

It is on a boat with a 15" transom (12 ft jon boat) BUT for some reason the motor claps on the outboard would not open up wide enough to fit over the transom so I built an adaptor for it out of a 2x4 and some clamps. This raises the motor 3 1/2" higher than it normally would be. The water pump is still submered when I'm sitting in back to steer so I thought it would be okay.

Maybe this is the problem. Also, is this motor a short shaft? How do I tell?

Thanks.

 

[R.Johnson]

Re: 1954 Evinrude sounding bad at full throttle

That 2 by 4 could well be the problem. If you put weight in the boat so it won't start to plane, what does the engine sound like?

 

[cc67]

Re: 1954 Evinrude sounding bad at full throttle

.

"Maybe this is the problem. Also, is this motor a short shaft? How do I tell?"

There would be a 5" spacer between the lower unit and the lower leg.

 

[jojo999]

Re: 1954 Evinrude sounding bad at full throttle

I would check for a broken (or partially broken) impeller or a clog in the intake. At higher RPMs problems can be caused that don't manifest themselves at lower throttle settings

.G
Argo Boat

 

[F_R]

Re: 1954 Evinrude sounding bad at full throttle

Thanks for the suggestion.

It is on a boat with a 15" transom (12 ft jon boat) BUT for some reason the motor claps on the outboard would not open up wide enough to fit over the transom so I built an adaptor for it out of a 2x4 and some clamps. This raises the motor 3 1/2" higher than it normally would be. The water pump is still submered when I'm sitting in back to steer so I thought it would be okay.

Maybe this is the problem. Also, is this motor a short shaft? How do I tell?

Thanks.

Well, no dad-gum wonder you are having slippage. If you had told us that right up front we wouldn't have wasted all this effort on false diagnosis. You gotta get it down into the water!!!!