Johnson slips/cavitates after 35 minutes

[swade28]

I have 1997 Johnson Ocean Runner 150 hp. It will run like a champ as soon as you put it in the water. After about 35-45 minutes it will shake/hesitate/cavitate/slip or something im not sure. It will only do it about 4000 RPM and if you decelerate its fine. Im not sure if cavitation or what but like i said it wont do it out of the gate. The prop is beat up some but i have a replacement that is new that i put on and does the same thing? Any suggestions. I feel like the mixture may be off some. Would that make since? Thanks, Scotty

 

[Walker]

Re: Johnson slips/cavitates after 35 minutes

First guess would be your lower unit is skipping. That is, your clutch dog is slipping on the forward gear. Could be as simple as a cable adjustment or as complicated as a L/U rebuild. One thing for sure. The more is does it the worse its gonna get and the more damage you will do to the gear and the clutch dog.

 

[swade28]

Re: Johnson slips/cavitates after 35 minutes

Ok. But why would it run fine for the first 30 or so minutes before any problems? And it does this everytime. Could it be a fuel delivery problem? Thanks, Scotty

 

[ob]

Re: Johnson slips/cavitates after 35 minutes

If you feel it may be a fuel delivery problem,one thing you could do is insure the fuel tank is venting properly.Does the fuel line primer bulb colapse when engine acts up?Do engine rpms increase ,decrease,or stay about the same when symptom occurs?Give as much detail as possible.

 

[walleyehed]

Re: Johnson slips/cavitates after 35 minutes

I'm going to throw in a hot ignition component, such as a coil, or even a sparkplug having high resistance at temp...Just a thought.

 

[swade28]

Re: Johnson slips/cavitates after 35 minutes

Not sure if bulb collapses or not, however the rpms jump back and forth as the engine is acting up. If it is the lower unit would i be better off getting new/used one or rebuilding it? Thanks, Scotty

 

[Walker]

Re: Johnson slips/cavitates after 35 minutes

If its your L/U it will seem like the motor is jumping into neutral for a split second. Follow Walleyehed's suggestions and check your ignition components, especially the coils. Inspect them for cracks and leaks and make sure the grounds are clean.<br />The better you can describe what its doing the easierm it is for someone here to diagnose the problem.

 

[umblecumbuz]

Re: Johnson slips/cavitates after 35 minutes

Sounds more like motor than LU. <br />You say the engine acts up?<br />I'd concentrate on the motor advice given here first and try to isolate the problem that way.<br /><br />Sounds too strange to me to be a LU if it always runs fine for the first half hour. Can't see a dodgy LU exhibiting those symptoms.

 

[swade28]

Re: Johnson slips/cavitates after 35 minutes

Its hard to describe what it does. But when it does act up its always on a warm engine and it only does it at 3800-4000+ RPM runs fine anything less than that. But it will be going along and starts to pulse you can feel it start surging forward/back repeatedly. Let off the throttle a tad and it goes away put it back down and starts to do it again. If was lower unit wouldnt it act up all the time anytime? Each surge the rpm will jump up/down. I honestly dont feel like its the lower unit, however, I did drain the lower and fuel seemed a little milky (seal?) and there were the tiniest shavings. Didnt even feel like metal. I couldnt even feel them they were like tiny pieces of threads. They were so small and so few i had to wipe them off the magnet i couldnt pull then off with my fingers. So now im really lost. Seems lower may need some attention but I dont feel confident that that is what is causing my current problem. Again I appreciate all your help. Also if is lower I would like to try the rebuild myself. Is it difficult? Thanks, Scotty

 

[swade28]

Re: Johnson slips/cavitates after 35 minutes

Hey Walker. You are in San Antonio. How about I swing by and pick you up and we go for a little ride. Then you will know exactly what is going on. Thanks, Scotty

 

[Walker]

Re: Johnson slips/cavitates after 35 minutes

Hey, I didn't notice you were here in SA. We can certainly do that. I'm in Leon Valley. 256-0200<br />I work for SAFD so I'm off or on work different days.

 

[swade28]

Re: Johnson slips/cavitates after 35 minutes

I wish that were the case for me. Seems Im always at work. lol. I hate to waste your time how are weekends for you? Maybe run out to medina or canyon one afternoon or something. Thanks, Scotty

 

[swade28]

Re: Johnson slips/cavitates after 35 minutes

"I did drain the lower and fuel"<br /><br />correction OIL not fuel. Thanks

 

[ob]

Re: Johnson slips/cavitates after 35 minutes

One other longshot is a spun prop hub.However I would think that would occur whether the engine was warmed up or not.That's a generous offer from Walker and sound help.<br /><br />BTW- Walker ,you didn't grow up in Corpus did you?I knew some Walkers whose dad was a fireman.

 

[swade28]

Re: Johnson slips/cavitates after 35 minutes

yeah prop has hub built in. And i have tried 2 diff props. Same problem. Thanks

 

[Walker]

Re: Johnson slips/cavitates after 35 minutes

No ob, been here all my life. I do get to the land cut every August though.

 

[Walker]

Re: Johnson slips/cavitates after 35 minutes

swade, you'll just have to call me. I work different days every week. No such thing as a weekend for me. I get 1 & 1/2 days off every 3rd. day

 

[swade28]

Re: Johnson slips/cavitates after 35 minutes

ok. I can do that. Also if you get a chance shoot me a line to no-golfin-fool@satx.rr.com and I can also get you that way. Thanks.

 

[swade28]

Re: Johnson slips/cavitates after 35 minutes

Would a broken gasket at the pick up unit in the fuel tank cause any of this. The gasket is shot. Guess I will go ahead and replace that as well. The screens are clean. Also I replaced the primer bulb but it doesnt ever seem to get hard. Doesnt seem as if it is doing anything really. Maybe the gasket? Thanks

 

[walleyehed]

Re: Johnson slips/cavitates after 35 minutes

Have you looked at your coils??? tested for spark???? Inspected spark plugs???<br />I may be wrong, but I think you need to take a look in that area.