Throttle issues- Mercruiser 250

[JMUDukes]

Hey...first post here on iboats...

I have a 24' sea ray with a Mercruiser 250 (that I just recently purchased). This past weekend I took it out for "sea trials" and on the way out, I opened up the throttle all the way with no problems. While we were out, someone got confused about which lever was SHIFT and which was ACCELERATE, so the engine revved a few times and got thrown from FWD to reverse without being throttled all the way down first. We anchored and went for a swim for a few hours. When we came back, the engine started right up w/ no problem at all, however when I shifted to FWD and throttled up, the motor revved up just like it normally would, but the boats could only get up to about 1/2 speed, even when it was wide open. I backed off the throtte and tried again, and it only got up to about 1/3 speed. It held steady there and got us home (slowly). The engine sounded fine/perfectly normal the whole time. When I came in to the dock, it shifted from FWD to Reverse without any problems, and we put it back on the trailer.


I have a few theories:
1. The oil has not been changed (apparently) in about two years. Possibly a clogged fuel filter?

2. Running out of gas? (The gas gauge is broken...we put in about 15 gallons before we went out, however there was no sputtering or anything that sounded like it was out of gas)

3. The stern drive may not have been lowered all that way (I have no idea if this affects it or not)

4. Something in the transmission broke during the SHIFT/ACCELERATE confusion (however it still shifted from fwd to reverse without any issues.)

Thoughts?

 

[gcboat]

Re: Throttle issues- Mercruiser 250

Sounds very simply like a spun prop. Take it to a repair shop and have them check it out. They can rehub it and it will be as good as new.

 

[JMUDukes]

Re: Throttle issues- Mercruiser 250

Pardon the technical ignorance, but what exactly is a "spun prop"? Most importantly, what do you think could have caused it?

 

[gcboat]

Re: Throttle issues- Mercruiser 250

Most larger boat props ( excluding straight shaft inboards ) are manufactured as a two piece unit. The hub ( which attaches to the motor shaft ) is one unit then the actual blades are 'bonded' to that hub. It sort of acts like a shock absorber. If you were to hit a large object while underway the prop is made to "break away" from the hub unit. It saves your lower unit from taking the direct force.
Now it's very possible that the sudden switch from forward to reverse broke that bond due to the inertia of the spinning prop. That's a lot of force being applied there.
Hope that clarifies it a little for you.

 

[JMUDukes]

Re: Throttle issues- Mercruiser 250

That makes sense. Thanks for the help...hopefully it won't be too expensive.

 

[Bondo]

Re: Throttle issues- Mercruiser 250

3. The stern drive may not have been lowered all that way (I have no idea if this affects it or not)

Ayuh,... That's My guess....
And,...
What's a "Mercruiser 250"

 

[JMUDukes]

Re: Throttle issues- Mercruiser 250

1) if it wasn't lowered all the way, it was lowered 90% of the way for sure.

2) if you open up the engine compartment, there is an I/O sitting there that says "Mercruiser 250" across the block.