TOPIC:

A worn out camchain, or stuck 'auto' chain tensioner gives a distinctive 'bunch of keys' rattle, seems to be most obvious rattle at about 3 or 4k. If it is a rattle directly related to the rpm then likely top end, a heavier knocking rattle could be a rod bearing.

Sometimes in a crash a bike can go down the road on it's side and the oil pump starves the main bearings temporarily, sometime later the unseen damage becomes apparent. Running them low on oil also kills the cranks.

Taking the cam cover off for a valve clearance check and general look around, and rebuilding and lubing the camchain tensioner would be a first step.

These 550 mills are cheap as chips, it may be better replacing then rebuilding.

i appreciate everyone's guesses but sad to say you were all wrong. when i pulled off the head, their was a small piece of metal inside number 4. it was magnetic. it has been smashed up a bit by the piston but it seems to have stayed on top of it. walls look good, no scaring. took me about an hour of frustrated thinking to realize that it had to pass through the carb. with the choke on, their are small, lets call them flappers, for each cylinder. you guessed it, number 4 was gone. i have no idea how it could have fallen off but it did. my bike is no race or show bike, just a poor mans cafe/bobber, so my plan is to clean her up, reassemble when my gasket kit comes in and ride on. thanks for all of your help everyone. especially wrenchmonkey

Wow! Didn't see that one coming. Sucks for sure but thankfully no serious damage. Glad you were able to dive in & figure it out Mass.
I recall another member here had a thread or link about this very issue - choke plate dislodging & how to modify it to prevent this failure.
Try searching. Sorry i forget who did it. Maybe Loudhvx, Patton or 650ed. Think it's actually about a 550...

This is a known common problem with the 550 choke flaps. Believe it or not sometimes they pass all the way thru or get mashed up.and spit out the exhaust. Member loudvx is our resident 550 expert her in my opinion. U really should search.out his 550 links on his posts. Great stuff. Helped me a lot.n R

choke flap is what I thought, a know fault on those.

Seems like you dodged a bullet if the cylinder walls are good. I have some used pistons if you get stuck - free, just cover the shipping, but you'll probably find some closer to home. Ideally get several and try to select the best fit.

The GPz and zx have slightly different pistons and higher compression ratio - although they would be an option too.

You'll likely be idling around 4 or 5k with the choke on missing that choke flap. (Mine's been doing it since I bought it) but you may want to replace it if you'd like to walk away from th bike while using th choke