I have a Suzuki vl250. It's been running great until last weekend I rode it home from work turned it off and the Mrs decided she wanted to go for a ride only problem is bike wont start! Since then I have managed to start the bike twice. The fist time it rode fine switched it off went back to it a few hours later and no go. I got it home on a trailer and a week later drained the float bowl and cleaned the plugs and boom she fired up. But after letting it idle for about 5 mins I went to give it a little throttle and it stalled and now wont start again. Motor tried to turn over and seems to have less enthusiasm each time I hit the starter button. Any ideas?
It sounds as though you float is allowing too much fuel in the bowl, which is in effect flooding the bike. When you said you drained the bowl and cleaned the plug and it fired right up is a typical sign of this happening. Also, after five minutes of idle time, stalling when you give it throttle, then not wanting to start could be a sign of dumping too much fuel as well. Like I said in my comment, a good running vehicle (near stoich) will have a light tan color. If it's black it means it's either getting too much fuel or is burning oil (a 2-stroke motor will have black plugs). Either the float is sinking (not sealed and taking on fuel) or the needle valve continues to allow fuel to come into the bowl after the float has seated it. I'd suggest getting a float and needle valve kit for your bike.
As for it getting more sluggish, I'd bet you are running down the battery with constantly trying to get it started. I'd suggest putting the battery on a charger and getting it up to full capacity and trying it again. I'll be you'll see a huge difference.