Rattles

[lordsexton]

I know this has probably been covered many times before but please bear with me.
My 1990 57000 miler had all the usual noises and rattles that I and many owners live with, but here's the thing. I did an oil and filter change using 15w40 mineral oil and she sounded like a bag of spanners! The noise was ten times worse. 2 days later I did just an oil change using Silkolene 10w30 semi synthetic motorcycle oil, it's a bit quieter but not as quiet as before I changed the oil the first time. It's the first oil change since I've owned it and was assured by previous owner of oil change 1500 miles ago, I've put another 2000 on her and have no idea what oil last owner used.
She tends to be noisier at lower revs and noise seems to disappear when clutch pulled in and just coasting.
It's putting me off riding her and she's my daily transport so any insights would be greatly appreciated.
Cheers
Andy

[Pat Conlon]

The major engine noise I've come across has been the chain rattle from the starter chain.
Not much you can do about that, until you split the case and install a new starter chain, something to consider at overhaul time.
The cam chain has an auto tensioner, so that stays relatively quiet.

Valve adjustments can take care of excessively loose valve noise.
Balancing the carbs smooths out the engine.

The big tip I've seen with engine rattles is to turn your idle up to ~1100 rpm.
Idling below 900 rpm the FJ engine sounds like a bag of bolts in the dryer.

I also run a heavier weight oil, a 20w-50 ester based synthetic due to the hot summers in my region.

[CutterBill]

Your first oil change, eh?  It's entirely possible that the PO, knowing that he was going to sell the bike, was using an absurdly thick oil to mask the engine noise. Isn't there a 60W oil for Harleys? 
Bill

[lordsexton]

We are having some unusually hot weather here in the UK Pat, might be a connection.
I must say the same thought occurred to me about previous owner Bill.

[simi_ed]

I know this has probably been covered many times before but please bear with me.
<snip>
I did just an oil change using Silkolene 10w30 semi synthetic motorcycle oil, it's a bit quieter but not as quiet as before I changed the oil the first time.
<snip>
Cheers
Andy

Andy, I think you already mentioned your problem.  10W-30 oil???  IIRC Yamaha recommends 20w-40 oil.  Randy recommended using 20W-50, as I recall. Too thin oil will surely add to the noise level!  As others have said, idle speed needs to be ~1,100 rpm as well. Try these and please report back.