Yep, sounds like thats your problem. 4 stroke bog on a slide carb. Could be the ap spring being inconsistent also,they're known to do that. The collective info on it is to install a merge racing ap spring and retune the ap so it runs consistent. There's other mods to get rid of it,but none are as permanent or reliable as the spring. http://www.mxrob.com/FCR_Install.htm. it's that's the bottom,about 1/3 of the way up. In short,take the carb off,fill the bowl,remove the cable cover, I removed the top cover and used the arm there to turn the throttle instead of the actual throttle wheel. Just lift the slide quick (pressure valve wont allow fuel to shoot if its too slow) and watch the fuel stream. You want it to barely miss the slide. You can adjust the screw on the arm that the throttle wheel contacts. Cant recall which way was to advance or retard it though. Or you can half ass it by leaving it on and just getting to the screw by the cables. IIRC a quarter turn was a good amount when it got close. Amazing carbs with tons of features and adjustments, unfortunately thats also their downfall when one goes wrong,needs serviced,or you just want something simple. I swapped my dr650 over to one,modded it to fit and use the vac petcock too...I'll be damned if I ever put the stock carb back on now.