My girlfriend just bought a used 2004 250 as a starter. It starts fine and runs with throttle; however, without throttle it dies. I tried adjusting the idle and noticed that the RPMs drop about every 15 seconds or so. My gut is telling valve/timing problem......????

 

even after you adjust the idle it dies huh?.... i would say it's timing.... did you buy it from the stealership like that? or was it a private party....

 

After raising the idle considerably (about 3500 RPM), it didn't die, but it followed the same pattern: correct RPM for a few seconds, then drops for a few seconds, then back up to where it should be, rinse, repeat. I noticed it on the road with higher RPMs too.

Bought it private party. The bike was a deal ($1200).....well, uh almost..... the first owner laid it over on a shoulder at low speed - usual scratches on the fairing & replaced blinker, no damage behind the plastic (gf wanted something she could drop in the parking lot a few times and not worry about as she's learning). Clean other than that. Hopefully, it won't be too expensive....

I'm guessing you're right about the timing....or perhaps the carbs???

 

I would take off the carbs and clean. Do not forget to remove the pilot jets and make sure they are spotless; they are the ones that control idle and slow speed.
After that if the problem persist vale adjust may be due.

 

I had a bike that did that once...ended up being a vaccuum leak from a split hose under the tank..... caused the exact same prob.

 

Good point, I always forget about those stupid hoses