I have a nasty spot in my carby's fuel delivery that is causing the bike to bog down. Any suggestions most welcome. Some background. The bike is an SR500 single, running a Mikuni VM34SS carby. This is a conventional carby but has an acceleration pump that sprays a little extra when required. The stock airbox has been replaced with a K&H slip-on filter and the exhaust is virtually straight-through. I've never had the bike running in stock trim - it was built like this so I've been guessing the settings from day 1. Stock settings are needle at groove 3 (of 5) and a main jet of #300. The recommended adjustments to accomodate the slip-on air filter and open exhaust are - machine 50 thou off the bottom of the carb slide, move the needle clip one position richer and to increase the main jet to #330. These were done. With that set up I get bogging if I snap the throttle open from 50% to full. The bike pulls very strongly in all gears up to 50%, holds road speed well and, if I open the throttle slowly fom 50% to 100%, the delivery is smooth. But settling at 50% and then openning it fast causes power loss for a second or two, followed by a recovery and gradual speed increase. I had some trouble with rough running at larger throttle setting - the bike would backfire on a trailing throttle so I dropped the main jet back to #310 - this fixed the backfires. But the flat spot was no different. I then lowered the needle to the stock position - this was worse so I raised it as high as it would go. Some improvement, but not good enough. Any suggestions?