1979 Johnson Javelin 100 hp slipping at high throttle

Hi. Engine started to slip at full throttle. Changed the prop in case it was slipping and still the same. I thought it may have been a cavitation issue when I trim up as I normally do to increase speed and that helped but then it started again. I checked the crank fluid and it was low. I'm thinking now it might be the gear set has warn to the point it might be slipping. Any other possibilities?

If it's the lower unit there would not be a smooth slip. It would likely be a terrible event. Maybe both props are bad. Is the prop you tried new....or has it been tested?

Have you inspected the boat bottom?

To be sure of what we're speaking of... The engine's model number would be helpful.

The 1979 100hp has a mechanical shift setup... capable of jumping out of gear, then being forced back in, which sounds and feels like one is hitting a underwater obstruction... BUT... having a internal problem resulting in "slipping" would be impossible unless perhaps the driveshaft splines stripped somehow. However, if that took place, the slipping would be permanent, not intermittent.

Has any work been done to the boat or engine recently... then shortly thereafter, this problem surfaced?

Possibly the rig (boat) has been trailered improperly, causing a hook in the keel that acts as a flap, raising the stern as the craft moves forward?

Or should the boat be stored at a marina (In The Water)... marine life may befouling the hull?

Has anything been added to the boat recently, modified in any way.... transducer, speedometer, something to the bottom of the hull or the transom that may be throwing a air pocket into the prop?

Is this craft new to you or a rig that you've owned for some time... and this problem just now popped up?

Thanks Joe and Gator. Those suggestions came to my mind too. This should be a simple fix. Damage to anti cavitation surface?

timguy said:

Thanks Joe and Gator. Those suggestions came to my mind too. This should be a simple fix. Damage to anti cavitation surface?

Click to expand...

Good to see you're still hanging in there Tim. Me?... Just visiting my ole favorite hangout, not a daily routine comeback attempt. I'm suspecting perhaps a mistaken model here, awaiting the model number. Take care, try to stay warm. Oh, just glanced at the back patio thermometer... 80 degrees Brrrr

Ha Joe! 30 here....forecast low near 10 tonight. Thinking on having a giant auction and bail out to move next door to you. This forum has been a blessing to me. Certainly deeply respect all my mentors here. You are the tops. Really glad to see your doing well and still helping our readers. This has gotta be a trim, setup issue....likely not 2 spun hubs.

Hi, Thanks all for the replies. Model is 100 TLR79S. I have owned the boat for 15 years. No changes to the hull, but late in the season some seagrass and fouling happening but not too bad. I try to get out and clean it so it has been worse. I normally trim the engine up once I get going to get a few more knots out of it. It is only a 100 HP for a 20 foot boat so a little under powered. As it sounded like excessive cavitation, i trimmed down and went away. Took it out of the water and low in gear case oil. Changed that out and put back int he water. Same issue so I figured it was bottom fouling. Last time it was worse and slipping at higher throttles regardless of trim position. IF the gear and spline has rounded? Is this a very difficult job. Not sure how to get to it to replace.

I noticed two tapped holes. What are these for. Someone else at our club had a piece with bolts in these. His was a newer V6 OMC

To grab the carrier and extract it after inner bolts are removed. Some carriers are held in place with spanner nuts.

There are 4 bolts way inside there , you take those out.-----Then those 2 threaded holes can be used to pull the bearing carrier out.----Yes newer gearcases use 2 threaded holes similar to those to hold the bearing carrier in.-----And I think the older gearcases using the 4 bolts are better !!!

Good info. Did the OP note what the grease looked like? Filings mixed in????