Stock jetting is lean especially on the slow jet. Can move up to a 45. A 45 slow and 120 main is the standard if the air snorkel is removed.
The "Shop Notebook", lots of good info on these bikes in here. https://docs.google.com/document/d/1mEsw891e5HUdLIrq4yYQzm2QCsRgK-ihDkrL_fu7_iA/pub#h.liicsytlw4nn
'05 needle: 16012-KPS-901
120 main: 99113-GHB-1200
118 main: 99113-GHB-1180
45 slow: 99103-MT2-0450
I am using the 118 main since I am usually riding at 5000ft or higher. I removed the air snorkel but did not mess with the muffler at all. The bike runs well, has plenty of power and is very quiet. I will take quiet over a few % more horsepower any day. Riding through the desert or even neighborhoods, people don't even notice you. That's a good thing.
The Seat Concepts seat makes the bike much more comfortable for longer rides. https://seat-concepts.myshopify.com/collections/2014/products/honda-2003-16-crf150f-230f-230x?variant=20638883078
Lube swing arm and linkage bearings as well as fork head bearings.
oil: 10w40 every 1000km / 30hours. a semisynthetic motorcycle oil is cheap and safe. 1.1qt capacity. Rotella T6 synthetic oil for diesels works great.
air filter: clean and lube when dirty. check it at least every 5-10 hours (after any ride if you ride in mud and sand).
chain: clean and lube after any ride. Wd40 is not a good lubricant. prefer a specific lube. a spray or, better and cheaper , an high viscosity gear oil.
slack should be 1 inch with the bike on the kickstand (push down and measure from swingarm, push up and measure from swingarm. difference should be 1 inch)
valve clearance: every 2000km / 60hours
brake oil: once a year
plug: once a year
tire pressure: every 15 days
fork bleeding: every month
I have been very happy with this setup for primarily offroading around Arizona, with some pavement riding:
Front: Kenda Trakmaster K760 (80/100-21)
Rear: Kenda Trakmaster K760 (110/100-18)
Pirelli MT16 for front and rear is another recommendation I saw.