Hanging idle is what you described where RPM's do not drop like they are supposed to or are slow to drop. Seen many a bike with a vacuum leak which will cause hanging idle. This could also cause the other issues you are talking about.

 

Yup theres a vaccum leak. Take it to a shop and have them smoke test the system if you can't find it.

 

The last bike I worked on with a vacuum leak that affected, was the boots that connected carb assembly to head.... all 4 boots were old and even though they looked good, once changed them out, Bob's your uncle. In that case, the bike sat unused for about a year in the Florida heat outside in a covered carport. The rubber dried out.

Those are a heavy rubber compound that can get brittle and may have small cracks not visible but can most definitely be there.... another place to look that I have found to be problematic is the caps on the ports for synching the carbs.... seen those crack badly and even missing on bikes. I would start with those and see if changing those out might be a help since those are cheap and should be easy to find or make your own. If those ports are not covered, they act like a vacuum leak.

 

Thank's for Your help guys! (and sorry for necro - didnt had time for anything except wedding for last few month's).
At last I've got some more time to do motorcycle stuff, problem is still unsolved and spring is around the corner.
I'll definitely check the hoses, but I'm not sure if that's it, couse sometimes (especially when it was cold outside) everything worked as it should, if there would be any leak the problem would occour every time, wouldnt it?
I started to wonder if it can be related to faulty FPR (fuel pressure regulator). What's Your thought's?

 

Well, assuming it was your wedding, congrats! Also, for following up! So many threads just... end, with no resolution!

I've seen temp cause some weird conditions on all motor vehicles, so it's always best to go ahead and check the obvious stuff first, i.e. the vacuum hoses. As for the FPR, I'd say that's unlikely based on the symptoms you've described but maybe check if the hoses all check out...

 

Yes, it was mine, thank You very much.
As I said, I'll try everything that Im able to but the question is why the problem occured randomly?
When I check it last time, about month ago, iddling was fine.

 

You're welcome!

Could just be that the rubber is old and starting to crack or slipped just enough to allow air in. My Forester developed a pinhole radiator leak that only occurred below 40F. Took me forever to figure it out!

 

Yesterday I switched fuel prssure regulator and all vacuum lines for new ones and.... it's maeby to early to say because it's still cold outside (around 2 C) but the bike runs like crazzzzyyy! I suppose that the issue is resolved, thrtottle response is way better then it was before, same as acceleration.
To my suprise, when accelerating front wheel went up quite high, I had to close the throttle, was not expecting that on this bike. It was sometimes happening when there was bump on the road or something, but never on that particular road and not as high.
Thank's for all responses and help. Hope that this thread will help ppl with similiar issues, I would suggest to start from vacuum lines, they are cheap and rubber parts in a motorcycle that is xx years old should be changed anyway.

 

Congrats on the fix!! Great feeling.

 

Front wheel goes up under acceleration? On an f4i? Do you have quick action throttle or something? My bike never lifts the front. Just a hint of shenanigans that's it. I am not a heavyweight at 80 KG as well