125 hp merc acts like its jumping out of gear.

dieselbird · Sep 28, 2010

I have a 2000 125 hp merc saltwater series that acts like its jumping out of gear.

I can apply full throttle at start off and rpm's will begin to build from 4700 and gradually, as the boat begins to plane off, the rpm's will go to 5200 and the boat is just about on plane and then all of a sudden it is like it has popped out of gear. rpm's will hit rev limiter and boat will decelerate. this is where it gets wierd. If I drop rpm's back to 2500 the boat will continue to move , but at a very slow pace, until I drop rpm's back to about 1000 and then it'll (lock up) again and I can apply full throttle until it builds speed again and the same thing will happen all over again. Also if I want to keep rpms down to 5000 or so I can run all day at about 20 mph

prop hub has been changed. lower unit has been taken apart and rebuilt by a merc dealer. motor continues to pump water.

I have $1200 spent allready and I'm about to junk it and look for another engine but this one works well if I could solve this problem without too much more money

oldgradywhite · Sep 28, 2010

Re: 125 hp merc acts like its jumping out of gear.

Sounds like your lower unit wasn't fixed right. Sounds like a classic bad lower unit.

Mi duckdown · Sep 28, 2010

Re: 125 hp merc acts like its jumping out of gear.

I would be back to the Merc dealer for some answers. 1200 bucks. It better run like a rapped ape. I'd be pissed

Faztbullet · Sep 28, 2010

Re: 125 hp merc acts like its jumping out of gear.

Sounds like severe cavation(obstruction in water flow) pinion splines or crankshaft splines stripped. I just had a 3270 Esprit with twins that started overheating problem and it the new bottom paint was too rough putting air bubbles in water pickup path.

Mi duckdown · Sep 28, 2010

Re: 125 hp merc acts like its jumping out of gear.

now that reread the original post. It does seem like a cavation problem.
Does this boat have a jackplate?
Pics would be nice.??
For 1200 bucks THE mechanic/ owner of the shop would be next to me on the boat for a test ride.

199675hpforce · Sep 28, 2010

Re: 125 hp merc acts like its jumping out of gear.

Better check lower unit shifting can you do thermo install same process adj shift link. This is done with motor off STATIC. Turn prop by hand to check find neutral spin prop, find first click for forward spin prop find first click for rev spin prop. You should beable to figure that out if thats problem. Adj screw on motor around 2 inches long

Dave1027 · Sep 28, 2010

Re: 125 hp merc acts like its jumping out of gear.

Maybe it's a spun prop hub?

starcraft1982 · Sep 28, 2010

Re: 125 hp merc acts like its jumping out of gear.

I would kindly walk in to the merc dealer who worked on your lower unit,explain the situation,kindly point out the warranty(i hope is there)and say come on,we`re going for a ride.Point out the issue and also the good advice given thus far on here about cavitation possibility,lower possibilities and have them correct it,regardless of what issue it turns out to be.Surely they can check your motor height,etc.Give them the chance to make it right.Your warranty and your $1200 bill says it should be. No reason trying to figure it out yourself when you have a shop basically obligated to make it right,if it is an actual lower unit problem.JMO

CharlieB · Sep 29, 2010

Re: 125 hp merc acts like its jumping out of gear.

Is it safe to assume that this is a New problem to a boat that you have had for a while and not a new-to-you boat that you are sorting out?

If you have have the LU into a shop for repairs, what ELSE have you done to the boat/LU/prop during the down time? New bottom paint, fittings, trim tabs, prop?

Pictures of the drive (down) while on the trailer could be very helpful.

dieselbird · Sep 30, 2010

Re: 125 hp merc acts like its jumping out of gear.

Charlie,
I just bought this boat from a guy who only had it for a couple of weeks. the reason he got rid of it is because of the problem I am discribing.
In saying that I stole the boat from him for that reason, thinking I would get it fixed for $1000- $2500.
why I am responding to you is the guy I bought it from told me that the guy he bought it from had just painted the bottom of the boat and the finish he used is very rough. looks like automotive (rock guard) to me, or the same finish anyway.
like I said before, it is definately not the prop hub or lower unit. wouldn't the lower unit eventually blow apart after several overrevs and jumping in and out of gear, or at least show some sort of wear(fillings) in the oil.
I am very curious if the rough paint on the bottom of the hull could possibly cause something like this to happen (so suddenly?)
thanks for all your help

dieselbird · Sep 30, 2010

Re: 125 hp merc acts like its jumping out of gear.

Sorry it was faztbullet not charlie that mentioned the paint issue

j_martin · Sep 30, 2010

Re: 125 hp merc acts like its jumping out of gear.

If you hang your nose over the transom when it's flying, the water between the pad and the engine should be smooth and clear. I'm willing to bet it's foam on your boat. You need an airplane propeller.

Faztbullet · Sep 30, 2010

Re: 125 hp merc acts like its jumping out of gear.

Yep rough bottom will do it....

CharlieB · Oct 1, 2010

Re: 125 hp merc acts like its jumping out of gear.

Ditto, sand that bottom and repaint with SMOOTH bottom paint that is intended for a planing boat.

That rough stuff that is on there is more likely for a displacement hull that never gets to the speeds of a planing hull, causing aeration of the water before the prop, which in turn is causing the prop to 'blow-out', cavitate terribly, and you loose all thrust until you slow enough for all the bubbles to rise away from the prop.

You may have gotten a great deal on the boat, you just need to re-finish the bottom to get back to a smooth finish.

starcraft1982 · Oct 1, 2010

Re: 125 hp merc acts like its jumping out of gear.

Wow.actually kinda hope the paint isnt the issue since that would mean a shop nutted you for $1200 rebuilding a lower unit that wasnt bad!

jimg984 · Oct 1, 2010

Re: 125 hp merc acts like its jumping out of gear.

lower the stop pin and tilt motor down more and be happy

125 hp merc acts like its jumping out of gear.

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