Engine knock

[Sbushman]

I could really use some help here. Here's the whole story. 1977 slickcraft ss 235 with a omc 190. First time out the boat would shutter between 600 and 900 rpms. Then it would die at 1000 rpms. Could power through every once and a while. But when I did the rpms would fluctuate. So I rebuilt the carb. All other issues were resolved. But now I have a knock at higher rpms with a load. With no load there's no knock. It only knocks over 2000 rpms and under load. I have no clue where it came from. Like I said it wasn't there before the carb rebuild. Any ideas what is going on? Please help.

 

[alldodge]

Starting another thread is not the way to get an answer.
http://forums.iboats.com/forum/engi...board-engines-outdrives/10444097-engine-knock

What you should do is post BUMP on this thread, same folks looking

Noises over the net is hard to describe but if its an actual knock, then you have probably spun a bearing. Need to make a vid or other recording and post

 

[Sbushman]

Sorry. Still kind of new to this. Thought I was in the wrong spot before. I'll try to get a recording of it soon. If it is a bearing why would it only knock on a load at high rpms and not wit out a load?

 

[southkogs]

Lifters? Have you done any work on the head recently?

 

[Sbushman]

I haven't done anything besides the carb rebuild. And like I said, the knock wasn't there before the rebuild. That's why I'm so confused.

 

[alldodge]

If unable to record and post, maybe find something on you tube which resembles kit

 

[Sbushman]

I have tried looking/listening for the same sound but can't find anything thats close. I forgot to mention that it sounded like it was coming from the area of the 3rd and 4th cyclinder. So from what I read it sounds like a pre ignition or detonation. But I don't know what would have caused that just from rebuilding the carb.

 

[alldodge]

Pre ignition is caused by incorrect timing and/or to little fuel. So if rebuilding the carb is causing the motor to get to little fuel, a knock will be heard under load. Pull the plugs and see what they look like. If they are white then you have a lean condition, they should look sort of tan. Check you timing

 

[Sbushman]

Ok. Do you know what the timing should be set at?

 

[alldodge]

I'm finding 10 BTDC, point gap .014-.019 dwell 31 degrees
http://www.maxrules.com/fixomcstern_specs.html

 

[Sbushman]

Ok. Thank you very much. Unfortunately I won't be able to run it until friday. But I'll let you know how it turns out. Thanks for all the help.

 

[Sbushman]

Well I finally got my boat out again and there was still a knock. But after about 5 minutes of running the knock just went away on its own. So I have no clue what the issue actually was. Ivins that it went away on its own I'm kind of thinking it was just fuel related. But I have no way to know for sure.