I've been having an issue with my 2011 Ninja 650R, and I was looking to see if anyone could offer up any ideas as to what the problem could be. When the bike idles, it does not hold constant RPMs, it will fluctuate from about 1200 (where I set it) to about 500, and will occasionally stall while sitting in idle. When I begin to move, it struggles to not stall on me. I have to open the throttle, sometimes quite a bit, before i release the clutch in order to get going. And even after the clutch is fully released it will take a second to fully get going with normal throttle response.

This happens occasionally when I switch into higher gears, but for the most part it's only a problem when starting from a stop in first. Some other potentially relevant information: I bought the bike used in January, and the previous owner may have let it sit for a while. He bought it brand new, and only put 1500 miles on it between then and January 2015. I put a Two Brothers exhaust on it not too long after I bought it. Also, I'm not sure if it's relevant or not, but it backfires quite a lot.

I brought it in for an oil change a couple weeks ago and asked them about it, they said it could be caused by water in the gas tank. I put some stuff in it to clean out the water, and it worked properly for a few days, then started acting up again. So I added some more and it worked for another half day. I brought it back to the shop the other day, and the impression I got from the mechanic I talked to was the only other thing he could come up with was there being a problem with the spark plugs, so they're supposed to be looking at it and let me know. But it seems to me there could be plenty of other issues other than the spark plugs. So I was wondering what else could cause something like this so I know what kind of questions to ask the mechanic when he eventually gets back to me.