First thought is a dirty jet that has you only running on 1 cylinder.
Fire up the bike for a minute or two, then carefully reach down to the cylinders, attempt to touch the cylinders and if one is "cold" while the other is hot, then you know which cylinder isn't running. By cold I just mean not the same as the other, it won't actually be cold.
Once you establish if it is only running on one cylinder, you can work over the carb or you might double check that your plug wires are securely snapped onto the plug/and or that the wire inside the cap has not come loose. You might also pull that plug from the cylinder and lay it on the head with the wire attached. Press the start button and see if the plug fires when the engine turns over. If it doesn't fire then you probably have an electrical issue. If it fires correctly then it's probably a fueling issue. If it doesn't fire correctly you might check to see that you didn't accidentally bump any of the smaller ancillary wires around the frame that could trigger the coils.
I once bought an M750 for $1,200 from Craigslist because the guy thought the clutch was toast and he recalled having a clutch replaced in a car once for a little over $1,000 so he wanted to rid himself of the bike. Too bad for him because a bike clutch takes minutes to replace. He fired it up at his place and I could feel that only heat was being generated in 1 cylinder so I bought it. I was going to buy it anyways. Got it home, fired it up and began riding it around the neighborhood. I had to slip the clutch and walk it from a stop to not kill the engine, but after a couple of minutes it cleared the jet and was back to running like a normal bike.
06 Paul Smart Sport Classic NFS ever.
08 S4RS Tricolore #081 NFS ever.
01 M600, aka, The Pink Monster
72 Norton Commando 750
03 KX60 just rebuilt the entire engine, with M600 rear shock, no wait now with S4RS rear shock...
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