hi ive got a 1988 fzr 400 got her running the other day for the first time as i bought it as a project, anyway on idle there just seems to be alot of engine noise, not knocking or anything like that it just seems like the engine its self creates alot of noise, im only comparing the noise to my 1990 honda nc29 which is really quiet on idle.

You think a oil change might sort her out?

Maybe an oilchange - didn't you do it before you started it up
Check the coolant level and change it if it looks dirty (there's a bleed bolt on the metal tube on the lower pipe. Coolant is fairly cheap use distilled water with it.

Could be the cam chain or the tensioner - it's on the back of the barrels below the carbs. Take it out and give it a clean with wd40 or light oil and a paint brush. Squash it in, put it back start the engine again.

ive changed the plugs and coolant but neglected to change the oil as it looked fresh, but the previous owner looked a bit of a monkey so he could have put anything in there for all i know.

I'd say it's more to do with the quantity to cut down noise as long as it's at the right level. cbr's are gear driven cams, as I say it could be a bit of camchain noise.

They are fairly noisey engines I find, the valves might need adjusting or carbs balancing for a smoother idle.
Mine is quiter when warm.

1988s probably a 3en1, (depends if the ram air intakes are above or below the headlights) so has the exup and these can rattle like a good um if not adjusted properly and it sounds like it's coming from the engine

compared to a honda they are a bit noisier, but that's just character