1978 Johnson 35 hp slipping

[jayhawk86]

Just purchased motor, on maiden voyage it slips at mid to high rpm, no clunking like clutch dogs, engages smoothly while shifting, let off throttle, start again is ok till mid rpm reached, plan on marking prop hub and checking tomnorrow, have old spline shaft, is there anyway to check hub in vice or can you not exert enough pressure,<br />also in regards to cavitation, both boat and motor are 20" transoms, can you still have a <br />cavitation problem?<br />thanks

 

[fireman57]

Re: 1978 Johnson 35 hp slipping

You are better off marking it. You are on the right track. Check this and let everybody know what happened. You saved a reply by two or three people by saying that you are going to mark the hub. As far as the cavitation problem does it sound like it is breaking loose or sucking air? As you said you just got this boat and have never run it before. I would bet that it had a spun hub when you got it. Post your results and the pros (not me) will be along to solve any problem you have.

 

[jayhawk86]

Re: 1978 Johnson 35 hp slipping

Put on different prop today since old one was chewed up pretty good, did mark new hub also and it's not slipping, still slips at mid to high rpm, what next? still smooth shifting and no clunking like a clutch dog slipping. I don't have my manual yet, are these electric or manual clutch, any help appreciated<br />thanks

 

[fireman57]

Re: 1978 Johnson 35 hp slipping

Are you sure that it is slipping and not cavitating? Where is you anticavitation plate in relationship to your stern? Is it above it or below it? Sounds like you might not be set up correctly. Walleyehead is good at this as well as a couple others. They should be along shortly.

 

[jayhawk86]

Re: 1978 Johnson 35 hp slipping

my cavitation plate is about 2-3" above bottom of boat, I know this is higher than the bigger engine I took off. Should it be level with bottom of boat?? I have my engine manually trimmed straight up/down,<br />thanks

 

[fireman57]

Re: 1978 Johnson 35 hp slipping

That is a little high. Usually start with level with the bottom. Once you get it there then try different trim settings until you get the hole shot and top end that you can live with.

 

[ob15]

Re: 1978 Johnson 35 hp slipping

The motor is too high. Can you lower it?

 

[jayhawk86]

Re: 1978 Johnson 35 hp slipping

No way to lower unless I would cut transom or build a different bracket on back of transom?

 

[fireman57]

Re: 1978 Johnson 35 hp slipping

You can get a jackplate that will let your engine sit out away a little from your transom and allow you to raise or lower it with a series of holes.