VF 500 throttle problem - please help

Hi.
I have a problem with my VF500, in neutral when I add throttle on the gas lever to about 3000 rpm and more and let go gas lever, the machine still takes a few seconds (3-5sec) revving and then slowly calm down.
On the carburettors have changed all the rubbers and o-rings even on the vacuum and manifold intake rubbers are changed. But nobody knows what the problem is, I do not have a fuel pump, fuel goes with gravity in the carburettor.
Throttle cables are ok and they are returning immediately in position.
Any ideas what is the problem?
Thanks in advance

 

Classic lean condition.

Candidate #1: About 1% of V4 owners can do a proper carb clean on their own. Something is still partially obstructed.

Candidate #2: When running spray some WD-40 (or contact cleaner , or something similar that won't damage paint if that's a concern) all over the intake rubbers and carbs. If the idle changes at all, you have a vacuum/intake leak somewhere.

 

thanks Captain 80s, I'll try with WD-40 for the start.
currently my tank is removed for painting but I'll try with plastic bottle or something.
thx