I have a gpz500s on a 2000 model, just taken bike for a test run and the bike is revving at 4000rpm with choke off and sitting in neutral,
Also once I got the bike going it wouldn't go above 50mph and it seemed to be struggling to get there.
I have only bought the bike recently and as I was told by the guy I bought it from my bike stood in a garage for about 12 years untouched
Please help if you can

Jason broadhurst, May 2016

Actually i have no idea what im talking about as for obvious reasons a bike with blocked carb jets wouldnt run very well at all let alone rev high,so a sensible person would say it has an air leak or is running weak,check the vaccum tap pipe is on properly and not split and check the carbs are fitted properly and the inlet manifold rubbers are not leaking or split.

griswold, June 2016

the carbs are probably gummed up with old petrol standing all that time especially if they weren't drained of fuel before storing, if the air filter's clean/new chances are the jets in the carbs are blocked, strip carbs and inspect each jet, might need new ones if they're really gummed up or soak in carb cleaner including the carb bodies as there's internal galleries that can get blocked, if that's not your game then send the stripped carbs off for ultra-sonic cleaning.

Grizwold, June 2016