Ahah! Its a Honda, never heard of it. A thumper no less. Got to agree with the look at the plug, sounds like its running out of fuel to me also. I think its not getting enough gas. There is a filter atop the petcock inside the tank, take the line loose from the carb, and run it in a jar to see if its flowing? Then you should pull the carb off, and the air box as long as your back there. How does the air filter look? Look for cracks in all the black rubber on the intake system. Take the bowl off the bottom of the carb, take all the jets out and clean it thoroughly. Check for worn parts, and replace the float valve and seat, its shot and will cause nothing but problems down the road. Hope you got a manual with the bike! If the plug is wet, you will have to do the same thing anyways. Vintage Bob