450r won't run or idle

[BigRedMachine]

My brother changed the jets in the carb and wouldn't run afterwards. We went back to the stock jets and air filter and it still isn't running. It's giving him a tough time just getting it started and when it does start, it dies right back out. Any help would be appreciated greatly.

[BigRedMachine]

Finally got it to run buts its loading up pretty bad so we're going to check the plug tomorrow. I'm still open to suggestions if anyone has any.

[04trx450R]

This motor is really sensitive to jetting ect,,, you may have fouled the plug, which is $16.00 by the way,, I went through a bunch of jetting problems, then just said screw it and got the HRC kit,,,, well worth it, it runs awesome with the kit, honda designed it that way, you know,,and you just follow some simple instructions