Need help! Boat Motor problem

[canon]

I posted a few weeks back about my 40hp evin. A few weeks back I took the boat out on the croix, kept the motor running for about an hour, fast and slow. On the way back when I opened it up, it would run for about 1 minute, then bog down and kill. When I tried to start it, it turned over really slow, like a low battery sound. If I waited for a minute, it woulkd start back up no problem, then drive it again and it would kill. If I threw it into neutral when it started to bog, the motor wouldn't kill.

Okay, that was a few weeks back. Saturday I took it out. I could not get the boat up to even half speed all morning, it would sputter like it wanted to go, but just wouldn't. After a while later, when I wanted to move couple hours later, the boat was able to get up to speed, but would then cut out again. NOW, anything past 1/2 speed, I get a loud rattle sound towards the lower unit, below the motor. Hard to tell exactly, but the motor sounds okay, the rattle seems lower. Any ideas of what could be wrong? I checked the lower unit oil, it is fine. I also get a nice stream of water comming out, so It should be getting cooled. Any ideas?

[Surface Tension]

Did you choke it when it bogged and was there an improvement?

If so fuel related. Check the fuel line, bulb and their connections.

Clean the filter.

Next step is a fuel pump and carb cleaning and rebuild.

[boatfixer]

I would check the compression and spark and go from there.

[Capt. Don*]

I know that the gearcase lube has been checked, but what are the chances that propshaft bearings or bushings are bad, causing siezing or tightening when heating up under load? I have had this happen once on a skiff in 35° water, we thought the engine locked up until we pulled the lower unit off.

[marine_man]

Per your previous post, I asked what your telltale stream was like, and if you had checked compression.

Any updates on those two items?

marine_man

[canon]

Thanks for all of the replies. I have a great stream of water coming out, I haven't checked compression. 1 thing that sticks in my head about all of this is why does it turn over very very slowly just after it quits, and why when I wait for a minute it turns over normal???? I think that is either one big symptom or side effect of what the problem is. Why this last time didn't it go over half speed but then did later, like 4 miles later? And why now the rattle?? I do most work on all my vehicles, lawn tractor, motorcycle ect, but I must admit I don't know anything about boat motors. Any help is appreciated.

[marine_man]

I would try Surface Tension's suggestion above to see if it's fuel related.

I'd consider having it compression tested to see what the status of the cylinders are.

marine_man