First Post - Fuel in Airbox

[claylev]

Hey gents,

So, about six months ago I bought a stagnate 2003 from a neighbor. It ran for awhile, albeit not awesomely - long periods of full choke to smooth (in the summer months and Southern California) and when I say smooth, it still wouldn't idle ALL the time (I got used to regularly rolling throttle at stop lights just to be sure). Checked idle adjustment and it was full-tilt upwards. The exhaust also backfired pretty regularly (although I'll be honest, this just made me smile because it made the 250 feel more "manly"). Fast forward a month ago and I decided to try and start'er up and switch over to her as my daily driver. She wouldn't start though, but she would crank until the battery would just give up. Tried a couple of times trickle-charging the battery and starting over but it seems like it lost it's amperage. Here's my admissions of various things I've done (stupidly or without enough knowledge to know better):

1) Attempted to crank over longer than 5 seconds
2) Probably didn't have enough gas at least some of those times
3) Since it's been 7 years since I've owned a non-Fuel Injection bike, I likely had the bike in any number of Prime/On/Off (In fact I can guarantee that I screwed this one up hard)
4) At some point I also decided to change the oil and did not change the oil filter
5) Replaced spark plug
6) Removed the tank at some point - I believe I reconnected everything right (followed the manual on this site) it's possible I did not.

So finally, I went ahead and got a new battery for her (well, used a battery from another bike) and she revved up like a madwoman. Not even a choke required. I also made sure she had plenty of gas in her. As I was visually inspecting a white smoke coming from the right side of the engine (as I write this, it makes me think head gasket? Guessing here) I suddenly noticed tons of fluid spilling onto the ground. Inspection followed it back to the airbox and it was MOST DEFINITELY fuel - the roommates won't stop bitching about the smell in the garage. I opened her up and then following one of the other posts on the forums I popped the airbox's drain on bottom and caught the rest of it. From here, I've pulled back my haphazard attempts at blinding firing at problems in the "maintenance" mindset and I'm now in the full on "Do nothing until you've verified everything" phase.

Here are the things I've done since reading here, researching through the various "rebuilding" bikes books I have, and the magic of youtube:

1) Ordered a new air filter (should be here soon...ish)
2) Following tips from the other related thread, and learning from this guy's instructional videos: - I've broken down my carb and begun cleaning it out. It wasn't what I might consider too dirty, but I'm being extra cautious here
3) Following one of his other videos, I've checked for a leaking petcock, but nothing there - seems fine

Here are my questions:

I want to make sure this (obviously) doesn't happen again. LUCKILY, this is a secondary "play" bike and it's not urgent, so I want to not just fix it, but i'd like to learn how to prevent things like this happening again. The youtube guy above has been helpful and so have the books, but since I'm a novice wrencher and I made so many early mistakes I'm just putting my toe in slowly and looking for help in the mean time. I have aspirations of really getting into this bike and fixing her up to gifting her to a friend of mine, so don't be afraid to give me the "here's what you should do to absolutely fix all the problems" answers. Money and time aren't much of a factor here, just experience.

Attached:
Image of bike when I picked it up - visually it's been decently maintained so at least it's got some hope
Image of airbox with fluid (fuel?) in it.
YOUTUBE: Video of the working-but-sucky idle from the summertime. Disregard any terrible narration:

-Clay