1978 evinrude 25 hp problem

[rards]

Would muchly appreciate if anyone could help me out,
i have just brought my first boat it is a 4 mtr tinny with a 1978 25 hp evinrude on the back, the bloke said he hadnt used it for a year or so. i took it out for the first time the other day to test it and it started and idles fine, pumps plenty of water. when moving slowly everything was ok but as soon as i increased the throttle a little bit every 5 seconds or so the motor would jolt and it felt like a had hit something on the bottom and the motor kept running , the more throttle i give it the harder it jolts, i didnt keep it in the water for long tho because i thought it might wreck the motor . i am hoping its only something minor but i have a feeling its not. any help would be muchly appreciated! thanks

 

[CatfishMN]

Re: 1978 evinrude 25 hp problem

Hi Rards, welcome aboard!

Sounds to me like it is a spun prop hub. This can be fixed by a lot of prop shops by re-pressing it, or by buying a new prop. You can test for this by putting a mark on both the inner and outer hub and repeating what you did when you took it out. If the two lines no longer match, you know you have a spun hub.

If it tests fine, then there may be some problems in the gear case. Let's hope it is a spun hub, eh?

 

[F_R]

Re: 1978 evinrude 25 hp problem

Nah, it is the clutch dog and forward gear. A prop will slip like spinning your wheels on ice, a dog will bang like hitting something.

There are about a bajillion of threads about the problem here, since it gets asked almost every day. Short story is the gearcase has to come apart and the dog and probably the gear must be replaced. Most people get in there and say it looks just fine. It isn't, or it wouldn't be jumping.

Not accusing you of anything, but the wear is greatly increased by trying to be gentle with shifting. That clatter you hear when slow shifting is the dog being beat to death. Correct way to shift is slow down to slow idle and shift with a quick, decisive movement.

EDIT: 316501 clutch dog is replaced by 390030 dog & cradle kit, $141.64. 389236 forward gear is replaced by 391085, which is replaced by 390972 gear and bearing kit, $326.64.

EDIT EDIT: The bloke probably knew that, and that probably is why he sold it. Too bad a first-timer boater got burned. I hope you got it cheap. Buyer Beware.

 

[rico suave]

Re: 1978 evinrude 25 hp problem

Actually I had a similar problem but it turned out to be the pin inside the gear case that holds the entire gear setup in position. If it's bent or cracked around that pin the gear assy moves back and forth within the case. It will eventually start popping out of gear once it gets worse. BTW, if that is what it turns out to be resetting the pin in liquid solder doesn't hold for more than a season or two and you'll need to have it welded in.