ok so I know this question has been asked before but I couldn't fine a post where they came back and said what it ended up being so I thought I ask again. so I have a 509 that was just built back in march it has dyno time and maybe 4 or 5 hours of run time. first time out the carb 1100 cfm ended up being to big with the lack of air in my engine compartment ran way rich. changed to 850 carb changed oil and spark plugs. it set for awhile then I took it out and started to here a knocking sound around 4000 RPM it made the sound a few time then when away and ran fine the rest of the weekend. about set for about a month took it back out two weeks ago and heard the noise again around 4000 rpm. oil still looks clean and stay at 75 to 80 psi and about 210 temp. any thoughts.

No way to even guess without hearing it.

Secondly, no decent engine builder would use an 1100cfm carb on a 509 marine engine.
I can't even believe ran right on a dyno.

I thought the same thing but it had Perfect afrs on dyno made 590 hp and 630 tq. Noise didn't start till after I put the 850 carb on I so I thought made it was a bit lean I change my jets from 82 to 84 and 94 to 96 have had a chance to run it yet.

How did you determine the 1100 carb was too rich?

yeah,,I would have found a way to get air into the engine compartment.

thats a loaded question,,,what do you think he should have used,,a quadrabog?he has a pretty stout motor.

Probably leaned it down now to the point its spark knocking , and good chance it damaged some ring lands, pistons, or rod bearings.

What is the list number on this 850 you installed ? Was it brand new ? Typically going to a smaller carb , will make the engine richer with all things equal. The dominators moved lots of air, but needed big jets due to booster signal.

Imo throwing a smaller carb on because it was "rich" , wasnt the proper fix.

It was dynod with a 1100? or was it a 1050/4150? Put the original big carb back on...hopefully you didnt hurt the motor.

Search function can help when the OP is loosely throwing around terms/parts used.

In reference to the 509, http://www.offshoreonly.com/forums/g...ml#post4259585

quoted below:

His last motor was replaced due to knocking also:
http://www.offshoreonly.com/forums/s...ml#post4152891

So maybe a rigging issue ? (fuel supply, exhaust, or etc ?)
Or tuning issues ?
Or engine assembly mistakes ?