I have a 97 Ninja EX250, and I am having a problem with one of my carbs. The bike is hard to start. If I choke it, it pops a little bit but never catches. If I take choke off, it pops a little more, but still doesn't catch. I have to hold the throttle about a third of the way open and crank for about 15-20 seconds to get it running. While cranking there is a gassy smell, which makes me think the bike is getting too much gas.
When the bike does fire up, you can tell that one of the cylinders isn't firing right away. I have to rev the bike to about 5k to get the second cylinder to pop to life, and when it does, it smells gassy and is rather loud. It seems to me like one carb is running extremely rich. I took the carbs apart a couple of weeks ago and cleaned them out and adjusted the floats. I checked the slide diaphrams and they looked fine. After putting things back together the bike ran fine. I went for a somewhat long ride this weekend and when I stopped near the end of the ride, the bike started having these problems.
At this point, I either suspect that one of the float needles is badly leaking or there is a problem with the vacuum slide. I did find that the clamps holding the rubber intake manifold on the left carb had come loose. I tightened them and this did not make a difference. I checked the vacuum hoses and all look fine. I have not yet checked for gas in the oil, but I am not sure if I would find much in there as I ride the bike multiple times per day.
Any thoughts or directions to look would be greatly appreciated.