Strange clunking noise at idle

Hello everyone,

Bought a not working FZ400N off a friend for cheap, the engine parts and design is alot like my previous XJ550 and a friends Xj600. Link: http://www.motorcyclespecs.co.za/model/yamaha/yamaha_fz400n 84.htm

Anyway, I have the bike running like it's meant to apart from this strange clunking sound coming from the engine while idling. Diving deeper, it goes completely away once the clutch gear is taken off from the engine. Install it back and it sounds like a main crank bearing is about to go. Uptil now I've looked into the clutch basket, basket gear, secondary driven gear that runs the clutch, all bearings, oil pump gears and its pin. There is absolutely nothing broken or worn in there.

Since loading the secondary driven shaft creates the noise, could it be the innards of either the primary chain, guides or the starter clutch?

 

Don't know much about the FZ400models, but here's some info on the XJ550/FJ600 models, which sounds like the same issue:


These non-symmetrical drive plates were supposedly an effort to reduce clutch noise, but it didn't work as well as expected, as some amount of clutch noise is common to XJ550 engines:

http://xjbikes.com/forums/index.php?threads/33497

 

My wife's '83 Shadow 750 has a knock that sounds just like a rod while idling in neutral. Put it in gear and the knock stops.

I've reached the conclusion that a shift fork is worn or bent and we hear the gear dogs banging against their mates while it's in neutral.