Welcome aboard,
Only use 87 octane or you will lose RPM'S, I didn't believe till I switched from 91 to 87 and got my RPM'S right back to 10.200-10.400, for the RATTLING part like you said up the IDLE and it'll be fine and for your sputtering and bog problem is DIRTY carbs if you don't use a good quality STABALIZER in your gas during the off season the pilots are so small on these they plug up with VARNISH a good cleaning and make sure to SYNC your carbs and she'll be fine drain all your old gas out of your tank and fill her up with fresh 87 octane and let her GO!!! you might also want to check your COILS for arcing and spark plugs while your at it.