I have a '90 4.3L OMC engine with a Cobra I/O.<br /><br />Recently the starboard manifold/riser clogged causing the manifold to get screaming hot and the exhaust hoses to burn. I removed the manifold,cleared the clogs, re-installed the manifold, and replaced the exhaust hoses. I noticed that there was no exhaust flapper seal in the exhaust pipe. The rod was there, but no seal. I bought and installed one. The assumption was that either one was never installed when the engine was installed new or that it had corroded and disintegrated. Water flow through the manifold is now fine and it runs cooler than the port side.<br /><br />Since then though, I've noticed a strange noise at all speeds from idle to full throttle. I thought it was an engine knock of some time, but have determined it to be coming from the carburetor. It's a hollow "wock" kind of sound. It's not consistent but happens a few times, stops, then happens again, etc. There is no apparent indication of a miss or lack of performance or overheating. The engine idles, shifts and runs OK. I don't want to ignore the noise since I've never heard it in the nine years I've owned the boat. Could this be a breathing problem? A valve problem? A fuel problem? Could it have anything to do with the manifold I re-installed?<br /><br />Any suggestions would be appreciated.
