Boat shudders and knocks

[stsvt07]

I recently bought a 1999 sportcraft 231 w/a, with a Volvo Penta 5.0 GI duoprop. I brought the boat to be inspected, and it rode fine. Shortly after, the boat shakes/shudders between 1000 and 2500 rpm. The boat will not go higher than 3000 rpm at WOT, and a knocking sound can be heard coming from the motor at WOT. The motor is carbureted. The only thing I can think of is that it may need a new fuel pump. Any help is greatly appreciated.

 

[skydiveD30571]

Re: Boat shudders and knocks

There may be a few different things wrong, but I doubt a fuel pump will cause a knocking noise in the engine. I'd start with a compression test to verify the conditon of the engine block.

 

[stsvt07]

Re: Boat shudders and knocks

I guess that would have been good for me to mention. Everything checked out ok with the compression test, all cylinders were within 10% of each other. The only complaint stated in the inspection was a dirty bilge. Other than that, everything appeared to be working properly. I have been told that a weak fuel pump will cause shuddering, loss of power, lower rpm's, and a fuel system issue could cause a knock. I should also state that the shuddering vibrates the whole boat, and the knock (which sounds like someone is knocking on the inboard motor housing/cover/doghouse, whatever you wanna call it) happens roughly every 5 seconds.

 

[Don S]

Re: Boat shudders and knocks

with a Volvo Penta 5.0 GI duoprop.

I'm confused, you say it's a GI, which is fuel injected, then later on say that it's carbed. Which is it. Or is it TBI fuel injection? Do you have the engine serial number? It should be 10 numbers long.

I brought the boat to be inspected, and it rode fine.

Explain inspected? Did a mechanic check it out (compression test etc.), and if that is the case, did it ever work ok after that? It's possible he got some plug wires crossed or not installed properly, or cracked a spark plug.

 

[stsvt07]

Re: Boat shudders and knocks

I was pretty sure the engine is carburated, but it says 5.0 GI on the top cover. I never got a chance to even take the top cover off yet, so it may be FI. I can grab the serial # today. As far as inspected, yes, I paid a mechanic to overlook the entire boat and tell me if it needed anything. No, it never ran right after the inspection. I am in the process of changing all of the spark plugs, and possibly spark plug wires now. Thanks for the replies.

 

[stsvt07]

Re: Boat shudders and knocks

It looks like maybe the mechanic that inspected the boat crossed up the spark plug wires. I unplugged all of them and put them back the right way, and ut appears to be running perfect. I took the boat out today and got it up to 4500 rpm's at just under WOT. Thank you all for your help. By the way, the model number (I believe) is 4110186473 (the 8 may be a B). It also says 5.0 GI PWTR (the P could be an F). Thanks again, hopefully it is fixed, for now, and this wasn't just a fluke.