I've always been able to fix my bikes myself in the past 40 years but I have an issue now that I'm struggling to fix.I have a 1996 cbr600f3. The problem I've got is that when started and it's off choke, it starts to rev up to about 4k.
I've cleaned an synchronized the carbs and fitted new boots.Ive sprayed carb cleaner around the carbs and it's not got any vacuum leaks.
The throttle snaps back as it should
I'm thinking it could be the throttle return spring has weakened over the years.
Could anyone please shine any advice of what else it could be please and where I could get a throttle body return spring, it would be greatly appreciated.Thanks.

 

Is it not like the F2 with 2 throttle cables, pull open and pull closed? Has the pull closed cable snapped?

The other possibility that comes to mind is the choke return spring, the choke mechanism can be quite stiff an a weak spring will fail to reset.

 

Given what you've done, I agree I don't think it's a sync issue. I tend to agree with @Ed Harris , I would check both cables. I believe they would be a more likely culprit than anything else. The only other thing is, did you adjust your throttle stop screw? It's the little knurled **** by the fuel cutoff selector.If that is not set properly, it can cause symptoms like this. A word of caution, if you start turning it to see if it has any effect, there is no stop on it. So if you turn it too far out, the spring and washer on the end will fall out and dive down into the nether regions of your engine compartment. That will make for a bad day.

 

Thanks for the responses, it's very much appreciated. I've bought some new cables and they arrived today.
It is a push pull system and when I was lubricating the old ones and checking the tensions yesterday, to see if I could improve the reving to 4k issue, unfortunately with no success.
While I had the air box off I noticed that that the carb side cable attachment was springing back a couple of millimetres above the stop after the throttle was closed.if I forced the throttle closed it would hold a steady 1500 revs.The cables were properly adjusted and the throttle snapped back quick ,( This is what made me think it was the spring that pulls the throttle back at the car side).
Hopefully the new cables will sort it ,if not I'll try to get a new spring that controls the return.Thanks again for the replies, very much appreciated.