My generator is not producing any power how do I go by exciting the brushes

Try flashing the rotor it has lost it's resideual magnetism through sitting.
Disconnect the rotor field wires at the AVR or on the exciter/brushes. Note they are polaroty sensitive. Connect a 12V battery to F+ and F- (note polarity) and momentarilly power from the battery for a few seconds. DO NOT forget to disconnect the rotor/exciter field wires first or the voltage regulator will be damaged.

Disconnect the rotor field wires at the AVR or on the exciter/brushes. Note they are polaroty sensitive. Connect a 12V battery to F+ and F- (note polarity) and momentarilly power from the battery for a few seconds. DO NOT forget to disconnect the rotor/exciter field wires first or the voltage regulator will be damaged.

If it has sat, it may have lost it's rotor residual magnetism. Disconnect the rotor field wires at the AVR or on the exciter/brushes. Note they are polaroty sensitive. Connect a 12V battery to F+ and F- (note polarity) and momentarilly power from the battery for a few seconds. DO NOT forget to disconnect the rotor/exciter field wires first or the voltage regulator will be damaged. If it hasn't sat check voltage regulator, rotor resistance, and stator resistance, and for shorts to ground.

The voltage regulator for the generator is not work, replace it. Why, if there no dc voltage to excite the stator it won't any output. GB...stewbison

Did you flash the exciter since it has been sitting and after brush replacement?It has probably lost its charge and needs to be flashed with 120v, let me know and we can go from there

most generators you can polarize the brushs this is done by using a 12v. battery and a set of jumper cables hook to the battery and touch the brushs with the other ends it doesn't matter whicht side, but before you do all that check the connections at the brushs and see if they are loose or not making a good contact, i do hope that i was able to help you, thank you.

http://www.nooutage.com/pto.htm

1. Check for any blown fuse and replace. It can be traced directly from the output lines.
2. Check field excitation. The field excitation is supplied by the battery to the excitation coil through a pair of carbon brushes. If the brushes are worn out, no excitation field is supplied and no output is generated. Replace carbon brush if found worn-out.
3. Use an analog multitester to check the continuity of the carbon brush and the field coil.
   

Replace the sockets they have most likely gone bad, I have found this on a lot of generators I've worked on.

It is possible that your voltage regulator is shot but before purchasing the volt regulator try flashing the fields first and make sure the brushes and rings are clean.

Glad to hear it was easy :-)
Here is a link to my trouble shoot solution so that this will get marked as solved.