To add pep, change to a 13 tooth front sprocket.
If it is running ok, the easist thing to do is forget about the jet size & just ride it. How are you going to find out what jet to put in it?
Call the PO and ask if he rejeted it. Also ask what elevation he jetted it for.

 

Looks like you guys were right in thinking it must have been rejetted if it were running well with the modifications. I heard back from the previous owner and he did have it rejetted but can't remember what the change was. Good to know, saves me from spending $30 - $40 for a rejet kit. Thanks for the help.

 

If the plug was drilled on the fuel screw on the bottom of the carb someone has probably been in the carb.

 

Perhaps not, I bought the jet kit and about gave up once I saw that the fuel screw cap was off, but I kept going and that was the only mod that they did, granted I have stock exhaust and stock air box (snorkel attached)