Alberto,

You should be getting more RPM out of that prop. A little fuel mist is normal but a large amount of fuel is not and points to a regulator that is not closing properly. A misbehaving regulator will cause you a lot of grief. If you are comfortable poking around in the YS you might want to disassemble the regulate and make sure it is flushed out with raw fuel to clean out any debris. If you are not, then send it into YS and have them give it a once over. Given the age of the 91 it may need a little TLC and Richard and his guys run each engine before they send it back.

Also make sure your fuel is 20% oil content.

Pete