Wilsons Sandbox

I have a 2004 with 30K miles on it (although the engine was rebuilt under warranty at 17K after chunks of a doo were found on the magnetic oil drain plug). Last season it developed a knock, but the knock wasn't constant - sometimes the knock would go away after I fiddled with the cam-chain tensioner, sometimes when I asked someone to listen to it it wouldn't knock (shy knock?). It is a slow knock, knocking once for every half dozen or so putts at idle. Recently I encountered engine stumbling at highway speeds. My first thought was a carburetor issue. I dropped the bowl and checked that there wasn't any crud in the jets. I checked the diaphragm, which looked good, and replaced it anyway. I checked the vacuum overun diaphragm and that was ok. I checked the vacuum line to the petcock and the operation of the vacuum petcock and they were fine too. So I've ruled out fuel supply issues. I've also realized that it doesn't just occur at highway speeds, rather it occurs under loads to the engine. The engine starts and idles just fine and I can rev the engine in nuetral without any issues. However, under acceleration or trying to maintain highway speeds the engine stumbles and shudders dramatically. I took a screwdriver to the engine in stethoscope fashion to try to isolate the knock. As best I can tell the noise seems to be coming from the chain end of the cam area. I'm not sure just what the problem is, but I'm thinking it is going to be expensive -- Kevin Powers White Bear Lake, MN [Non-text portions of this message have been removed]